Volume 111, November–December 2023 American Scientist

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How the U.S. Census changed EARLY COMPUTING

Using lasers and ultrasound to SEE INTO SOLID OBJECTS

The stunning diversity of MOLLUSK SHELLS



AMERICAN

Scientist



November–December 2023

www.americanscientist.org

Taking Charge of Molecular Shape US$5.95

Positively charged zones can help predict chemical reactions and behavior.

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AMERICAN

Scientist Departments 322 From the Editors 323 Letters

Volume 111 • Number 6 • November–December 2023

Feature Articles

360

328 Spotlight Engineering for heat waves • Dandelions: diuretics and rubber • Poverty and neuroscience • Briefings 338 Sightings Uncovering ancient corrections 340 Perspective (Don’t) shut your π-hole Dean J. Tantillo 346 Technologue How Herman Hollerith counted America and the world Ainissa Ramirez

Scientists’ Nightstand

352 “Seeing” into Opaque Materials with Light and Sound Lasers can generate and detect ultrasonic waves that can image the interiors of solid objects. David M. Pepper and Todd W. Murray

368 Beautiful Armor The rich variety of mollusk shells reflects the diversity of the phylum, which has fascinated humans for millennia. Andreia Salvador

368

376 Books A quantum history of space-time • To fix the brain, look to other nerves • The power of data literacy

From Sigma Xi 381 Sigma Xi Today From the president: Of mice and mental health • 2023 Gold Key Award winner Shirley M. Tilghman • IFoRE session spotlight • Faces of GIAR: Abhinav Sur • 2023 Sigma Xi Fellows

352 360 Memories Within Myth The stories of oral societies, passed from generation to generation, are also scientific records. Patrick Nunn

The Cover Collagen is the body’s most abundant protein, strengthening bone, teeth, tendons, skin, and the support sheets of the internal organs. Its ropelike structure comes from winding three stands of amino acids into a triple helix. The amino acids are linked together with amide bonds that include carbonyl groups (carbon–oxygen double bonds), and the strands wind into helices because of charge interactions between different amides along the chain. The positively charged regions around the carbon atoms in carbonyls are called π-holes, and they’ve sparked spirited discussions among chemists about their origins. In “(Don’t) Shut Your π-hole” (pages 340–344), Dean J. Tantillo argues that the debates are productive if they help chemists design experiments to build better drugs, materials, and more. (Illustration by David Goodsell.)

From the Editors

AMERICAN

Scientist

Talk It Out

www.americanscientist.org VOLUME 111, NUMBER 6

E

ach discipline of science has its own debates in which evidence for one side or the other may not be particularly clear, because evidence can often be interpreted from different perspectives to support diverging conclusions. Sometimes there is more than one answer and both sides are right. And sometimes neither side is correct; the answer may lie at a point in between—or somewhere else entirely. The best approach that scientists can take is to give space to all theories that have sufficient evidence to merit serious consideration, and to expect that future work will continue to build the cases for and against those theories. At times, the debate itself can lead to advances. In this issue’s Perspective column, “(Don’t) Shut Your π-Hole” (pages 340– 344), Dean J. Tantillo informs us about one such debate within the world of chemistry. Molecules that have a neutral charge overall are nonetheless made up of elements and electrical bonds that create regions with more or less positive charge. Areas that are lacking electrons are termed either π-holes or σ-holes, depending on their shapes. But what causes “passion-filled debates,” as Tantillo says, is defining what areas of the molecule really constitute a π-hole or a σ-hole, and determining how much these areas really mediate interactions between molecules. Tantillo believes that these debates are not only acceptable, but also fruitful, because they lead researchers to create new predictions that are then testable and can lead to new experiments, which in turn can have im322

American Scientist, Volume 111

portant practical outcomes, such as the development of a new cancer drug. Research into communication itself was behind the imaging development that David M. Pepper and Todd W. Murray discuss in their article “’Seeing’ into Opaque Materials with Light and Sound” (pages 352–359). Pepper and Murray discuss an early invention of Alexander Graham Bell, the photophone, which used sunlight to transmit voices. Bell observed what later came to be known as the photoacoustic effect, the formation of sound waves by the rapid thermal expansion and contraction of the air over a periodically heated surface. This effect underlies a current technique, laser-based ultrasound, which uses lasers to generate ultrasonic waves within opaque materials, the echoes of which are detectable at the material’s surface and can be used to create images of what’s inside. In “How Herman Hollerith Counted America and the World” (pages 346–351), Ainissa Ramirez recounts how a chance conversation played an important role in events that contributed to modern computing. At a cocktail party, Hollerith, an inventor with an interest in tabulating machines, connected with a prominent member of the U.S. Census Office, and they ended up discussing the technology needed for counting the population. Eventually, after years of experimentation and a number of setbacks, Hollerith realized his dream of creating a tabulating machine that would modernize the processes of the Census. His system, which used punch cards, tabulated the results of the 1890 census, and drastically shortened the amount of time it took to come up with a rough count of the census, from seven years to six weeks. Hollerith’s company later became part of IBM and the computer revolution. The history of science is full of stories in which a random encounter or a new perspective kicked off a major innovation or resolved a long-­ standing enigma. Have you ever had a serendipitous experience or an unexpected result that changed the direction of your research? Join us on social media or write us a message through our website to tell us about it. —Fenella Saunders (@FenellaSaunders)

EDITORIAL Editor-in-Chief  Fenella Saunders Special Issue Editor  Corey S. Powell Managing Editor  Stacey Lutkoski Digital Features Editor  Katie L. Burke Acting Book Review Editor  Jaime Herndon Senior Contributing Editors  Efraín E. RiveraSerrano, Sarah Webb Contributing Editors  Sandra J. Ackerman, Emily Buehler, Christa Evans, Jeremy Hawkins, Flora Taylor Editorial Associate  Mia Evans

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EDITORIAL ADVISORY PANEL Richard Boudreault, University of Waterloo René Fuanta, East Stroudsburg University Simson Garfinkel, AI2050, Schmidt Futures Sonya T. Smith, Howard University Caroline VanSickle, A. T. Still University of Health Sciences American Scientist gratefully acknowledges support for engineering content through the Leroy Record Fund. Sigma Xi, The Scientific Research Honor Society is a society of scientists and engineers, founded in 1886 to recognize scientific achievement. A diverse organization of members and chapters, the Society fosters interaction among science, technology, and society; encourages appreciation and support of original work in science and technology; and promotes ethics and excellence in scientific and engineering research. Printed in the USA

Letters to the Editors

Readers Remember Henry Petroski joked that at the time American Scientist had two columnists from Manhattan College. I miss him. Peter Denning Salinas, CA

Courtesy of Catherine Petroski

To the Editors: Thanks for your extensive and insightful essay about Henry Petroski. It is to his essay that I turned when I got a new edition of American Scientist. His prose was so clear and declarative. Henry’s subjects were varied and always engaging. I and many readers will miss him. Bob Chianese Ventura, CA To the Editors: I was the editor-in-chief of American Scientist when Henry Petroski wrote his first Engineering column in the ­January– February 1991 issue. I had read and been impressed by his book To Engineer Is Human (St. Martin’s Press, 1985). I really wanted to get more coverage of technology into the magazine, so I approached him about becoming a regular columnist. Henry was a little bit of a hard sell; he worried that having his work in the magazine would reduce sales of his books. But obviously he came around. Henry was such a reliable ­columnist— he always turned in clean copy on time. One day in the 1990s, we met for lunch. He had just published yet another book. I was grumbling about the slow pace of progress on my own first book. Henry observed: “When I first thought about writing a book, it seemed intimidating. But then I sat down and did the math. If you just get up every morning and write a thousand words, books get finished quickly enough.” Clearly, he was a man who took his own advice. I’ve always wished that I could have followed his example. Brian Hayes Chapel Hill, NC To the Editors: I was delighted to see Henry Petroski’s final column in the July–­August issue (“Building Knowledge”), and so sorry to learn he had passed on. He and I were classmates at Manhattan College. I saw him once at a reunion and we www.americanscientist.org

To the Editors: I am one of Sigma Xi’s oldest members (since 1961, and I recently turned 91— and still working), and I’ve known Henry since 1985. He was hugely important in my professional life, right up there with my meeting with Albert Einstein. On two occasions in the 1990s, I invited Henry to keynote a conference I was running—one on computer system trustworthiness and one on software engineering. In each case, his keynote made an enormous contribution to the entire conference. We had various ongoing communications, including discussions relating to his American Scientist columns. I submitted the following cover encomium for his last book, Force (Yale University Press, 2022): Henry Petroski is a true polymath with a superbly holistic perspective. This book is a unified field theory of almost everything, exploring the interdependencies among every­ day forces and their effects. Albert Einstein would have loved it. Peter G. Neumann Palo Alto, CA To the Editors: Indeed, we shall all miss Henry Petroski and his Engineering columns very much! My favorite (not surprisingly) dealt with bridges made of unconventional materials, including frozen tomatoes (“Frozen Tomatoes and Other Construction Materials,” May–

June 2022). Henry was kind enough to credit me by name with the germ of that idea, which derives from the only joke my late Uncle Roy knew: Why is an old maid like a frozen tomato? Because it’s hard ter-mate-er. I had last emailed him a question about friction prompted by his column, “The Push and Pull of Friction” (­November–December 2022). My question went unanswered, as did my final suggestion for a column on “Bridges in Song and Story”—the well-­designed (The Bridge on the River Kwai) and poorly designed (“London Bridge Is Falling Down”); the judgmental (The Bridge of San Luis Rey) and the nonjudgmental (“Bridge over Troubled Water”). I suppose I shall have to write that one myself some day! Virginia Trimble Irvine, CA To the Editors: I was so sorry to hear that Henry Petroski passed away. I always read and enjoyed his excellent articles on various engineering projects. I contacted him a number of times—most recently last year to share my experiences. He always responded to my emails. I will greatly miss him. Joseph A. Castellano San Jose, CA To the Editors: I am so sorry to read that Henry Petroski has passed. I was an avid reader of his American Scientist columns, as well as his books. The two of us corresponded frequently on a wide range of subjects. We were like minds—curious and interested in virtually everything we saw around us. We had other things in common—we were both Manhattan College graduates, and we reminisced about our times there. I am chemically- and mechanicallyminded and he was soundly structural, but as soon as I heard about the Florida condo collapse (June 24, 2021), I thought of the salt air corrosion of rebar, and the expansion cracking of concrete on the columns. Henry bravely wrote a piece on the subject before studies were com2023

November–December 323

As you mentioned in your In Memoriam article, he will be sorely missed, and you have made the right decision in retiring the Engineering column in his honor. Henry C. Brenner New York, NY To the Editors: Henry Petroski’s columns were always the highlight of my reading in each issue of American Scientist. You are right to retire the Engineering column in his honor. His remarkable contributions will be sorely missed by many, including me. Forman Williams La Jolla, CA To the Editors: I was quite saddened to read today that Henry Petroski had passed away. Tom Dunne His column was the one I immediately Henry Petroski’s Engineering columns sometimes gave a peek into his personal life, such as the challenge of replacing the chimney cap on his house (“Occasional Design,” January–­ turned to when I received the latest isFebruary 2010). The breadth of his interests appealed to readers of all backgrounds, and those sue of American Scientist. As a native of personal touches added warmth and developed a sense of kinship with his readers. Brooklyn, his article on the Brooklyn Bridge was particularly exciting (“Altering an Icon,” January–­February). pleted (“What Lessons Will Be Learned To the Editors: from the Florida Condo Collapse?” I am a retired university professor I’m very sad to see him go. ­September–October 2021), and those fac- and a physician. My undergraduate Paul Goldberg tors were high on his list of likely causes. degree was in chemistry, not engineerBoston, MA He also wrote a more lighthearted ing. But I earned a PhD in engineering piece on pesky light switches (“Solving (industrial, not mechanical) at age 60 Failures Around the House,” J­anuary– and taught it (as well as medicine) for To the Editors: February 2020). I wrote him a follow-up 10 years prior to retiring. One of my Thank you for remembering Henry email to that article, sharing a clue to the combined passions in engineering and Petroski in the September–October issues he faced—switches that do not medicine was quality and safety, and issue of American Scientist. I always have “off” and “on” written on them that was my connection with Henry looked forward to Henry’s columns, are the three-way type. And so on as we Petroski. I read all of his books and all and I have read and enjoyed many of of his columns in American Scientist. wrote back and forth over the years. his books. I corresponded with him Although I never met him, I always twice: once about his article on newsThomas F. McGowan felt that we were “kin.” I will look paper folding (“Industrial Origami,” Atlanta, GA forward to future articles in American January–February 2005) and once conScientist, but it will most certainly be cerning his article on the history and different without him. I join the many design of can openers (“Bottle and To the Editors: Can Openers as Levers,” March–April Like many readers of Henry Petroski’s who will deeply miss him. 2017). In both instances, I received a column, especially those of us profesPeter J. Fabri sional engineers, I was deeply sadpersonal and pertinent written reply. Tampa, FL dened to hear about his passing. Joe S. Herring As an American Scientist subscriber Rockport, TX and reader of his books, I have greatly To the Editors: enjoyed and learned a lot from Henry’s I was very sorry to learn of the passing insights. I wrote him an email once of Henry Petroski. His column was my about my views on the philosophical favorite in your magazine, and whenev- How to Write to American Scientist aspects of practicing engineering. He er I received a new issue I would quickly Brief letters commenting on articles wrote back within 24 hours with a very turn to Engineering and read it first. In appearing in the magazine are welpositive response. That was most ap- 2017, I wrote a letter to the magazine comed. The editors reserve the right preciated as I’m sure he received many in response to his article about the slide to edit submissions. Please include emails on engineering topics. rule (“Slide Rules: Gone but Not Forgot- an email address if possible. Address: ten,” May–June 2017), relating my own Letters to the Editors, P.O. Box 13975, experiences with slide rules, electronic Research Triangle Park, NC 27709 or David Shteinman [email protected] calculators, and pocket calculators. Castlecrag, NSW, Australia 324

American Scientist, Volume 111

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Connecting Memory and Imagination

Felipe De Brigard, a cognitive neuroscientist at Duke University, discusses the connection between false memory, which is the psychological experience of remembering something that did not happen, and episodic counterfactual thinking, which is imagining alternative ways that past personal events could have occurred. www.amsci.org/node/5131 Change Is the Only Constant

Kristin Poinar reviews Elizabeth Rush’s book The Quickening: Creation and Community at the Ends of the Earth, which documents an Antarctic expedition to Thwaites Glacier alongside questions of what it means to decide to have a child in the face of climate change. www.amsci.org/node/5130 An Inside Look at COVID-19 Policies

If the Q&A with Linsey Marr in the September–October issue piqued your interest, check out

the companion podcast for a deeper dive into the evolution of COVID-19 responses. The Virginia Tech engineer spoke with American Scientist digital features editor Katie L. Burke about how research into the airborne spread of SARS-CoV-2 helped shape U.S. and international policy during the epidemic. www.amsci.org/node/5124

Canyon, but their adventure down the Colorado River has largely gone unnoticed. Melissa L. Sevigny’s book Brave the Wild River adds their contributions to the narrative. www.amsci.org/node/5129

Fall STEM Reads of 2023

Find new releases for your #ScienceSeptember book stack and beyond. www.amsci.org/node/5127

Check out AmSci Blogs www.amsci.org/blog/

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A Broader Look at Modeling

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The AmSci editors curated a collection of past content related to the July–August special issue on scientific models. www.amsci.org/node/5105

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Trailblazing Women Botanists in the Grand Canyon

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Spotlight | Climate change affects crucial technologies and materials.

Engineering for Heat Waves Higher temperatures cause machines to overheat, batteries to lose power, and roads to buckle, crippling infrastructure systems. Humans weren’t the only ones who needed to stay cool during 2023’s record-­breaking heat waves. Many machines, including cell phones, data centers, cars, and airplanes, become less efficient and degrade more quickly in extreme heat. Machines generate their own heat, too, which can make hot temperatures around them even hotter. No machine is perfectly efficient— all machines face some internal friction during operation. This friction causes machines to dissipate some heat. That dispelled heat mixes with the external temperature, so the hotter it is outside, the hotter the machine will be. Cell phones and similar devices with lithium-ion batteries experience decreased performance when operating in climates above 35 degrees Celsius (95 degrees ­Fahrenheit). This throttling is by design to avoid overheating and increased stress on the electronics. Designs that use innovative phasechanging fluids can help keep machines cool, but in most cases heat is still dissipated into the air. So, the hotter the air, the harder it is to keep a machine cool enough to function efficiently. Plus, the closer together machines are, the more dissipated heat there will be in the surrounding area. We are engineering researchers who study how machines manage heat, as well as ways to effectively recover and reuse heat that is otherwise wasted. Technologies for reducing, capturing, and reusing heat could help prevent mechanical failures and weakened infrastructure systems during an era of rising temperatures. Deforming Materials Higher temperatures, either from the weather or from the excess heat radiated from machinery, can cause materials in machinery to deform. To understand why, consider what temperature means at the molecular level. At the molecular scale, temperature is a measure of how much molecules are 328

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vibrating. The hotter the temperature, the more the molecules that make up everything from the air to the ground to materials in machinery vibrate. As the temperature increases and the molecules vibrate more, the average space between them grows, causing most materials to expand. Roads are one place to see this happen—hot concrete expands, gets constricted, and eventually cracks. This phenomenon can happen to machinery, too, and thermal stresses are just the beginning of the problem.

Waste heat from power plants could support 27 percent of residential airconditioning needs. Travel Delays and Safety Risks High temperatures can also change the way oil in your car’s engine behaves, leading to potential engine failures. For example, if a heat wave makes it 16.7 degrees Celsius hotter than normal, the viscosity of typical car engine oil can change by a factor of three. Fluids such as engine oils become thinner as they heat up, so if it gets too hot, the oil may not be thick enough to properly lubricate and protect engine parts from increased wear and tear. Additionally, a hot day will cause the air inside your tires to expand and raise the tire pressure, which could increase wear and the risk of skidding. Airplanes are also not designed to take off at extreme temperatures. As it gets hotter outside, air expands, making it thinner or less dense. This reduction in air density decreases the amount of weight the plane can support dur-

ing flight, which can cause significant travel delays or flight cancellations. Battery Degradation In general, the electronics contained in devices such as cell phones, personal computers, and data centers consist of many kinds of materials that all respond differently to temperature changes. These materials are all located next to one another in tight spaces. So as the temperature increases, the types of materials deform differently, potentially leading to premature wear and failure. Lithium-ion batteries in cars and electronic devices degrade faster at higher operating temperatures. Heat increases the rate of reactions within the battery, including corrosion reactions that deplete the lithium levels, which in turn reduces the battery’s storage capacity. Tests conducted by Recurrent (a company that provides car and battery information for the secondary electric vehicle market) found that electric vehicles can lose about 20 percent of their range when exposed to sustained 32-degree-Celsius (90-­degree-Fahrenheit) weather. Data centers full of computer servers dissipate significant amounts of heat to keep their components cool. On very hot days, fans must work harder to ensure chips do not overheat, and in some cases, powerful fans are not enough to cool the electronics. When the data centers need a stronger cooling system, they often turn to evaporative cooling. This method sends incoming dry air from the outside through a moist pad. The water from the pad evaporates into the air and absorbs heat, which cools the air. This technique is usually an effective and economical way to keep chips at a reasonable operating temperature. However, evaporative cooling can require a significant amount of water, which is problematic in regions where water is scarce. Water for cooling can add to the already intense resource footprint associated with data centers. Air conditioners struggle to perform effectively as it gets hotter outside— just when they’re needed the most. On hot days, air conditioner compressors have to work harder to send the heat from homes outside, which in turn disproportionately increases electricity

Paul Smyth/Alamy Stock Photo

A heat wave in July 2022 caused major cracks in a roadway in Kingston upon Thames, a town in Greater London. Concrete expands in high heat, as do many other materials crucial to infrastructure and technology. Engineers and materials scientists are studying ways to manage increasing temperatures, including how to capture and reuse expended heat from machines and other devices.

consumption and overall electricity demand. For example, in Texas, every increase of 1 degree Celsius creates a rise of about 4 percent in electricity demand. Heat leads to a staggering 50 percent increase in electricity demand during the summer in hotter countries, posing serious threats of electricity shortages or blackouts, as well as higher greenhouse gas emissions. Reusing Heat Heat waves and warming temperatures around the globe pose significant shortand long-term problems for people and machines alike. Fortunately, there are ways to minimize the damage. One is to ensure that machines are kept in air-conditioned, well-insulated spaces out of direct sunlight. Another is for consumers to use high-energy devices, such air conditioners and electric vehicle charging stations, during off-peak hours when fewer people are using electricity. Individual changes at the consumer level will not solve the problem alone, so scientists and engineers are developing ways to use and recycle the www.americanscientist.org

vast amounts of heat dissipated from machines. One simple example is using the waste heat from data centers to heat water. Waste heat could also drive other kinds of air-conditioning systems such as absorption chillers, which use heat as energy to support coolers through a series of chemicaland heat-­transferring processes. In both of these examples, the energy needed to heat or cool something comes from heat that is otherwise wasted. Indeed, one of us (Garimella) collaborated on a 2011 study that found that waste heat from power plants could support 27 percent of residential air-conditioning needs, which would result in a dramatic reduction of overall energy consumption and carbon emissions. Extreme heat can affect every aspect of modern life, and heat waves aren’t going away in the coming years. However, there are opportunities to harness extreme heat and make it work for us. References Barré, A., B. Deguilhem, S. Grolleau, M. Gérard, F. Suard, and D. Riu. 2013. A review

on lithium-ion battery ageing mechanisms and estimations for automotive applications. Journal of Power Sources 241:680–689. Calama-González, C., et al. 2023. Thermal insulation impact on overheating vulnerability reduction in Mediterranean dwellings. Heliyon 9:e16102. Hough, B. 2023. Summer survival guide for electric cars: What A/C does to your range. Recurrent (July 13). recurrentauto.com/research /what-a-c-does-to-your-range Ndukaife, T. A., and A. G. Agwu Nnanna. 2018. Optimization of water consumption in hybrid evaporative cooling air conditioning systems for data center cooling applications. Heat Transfer Engineering 40:559–573. Obringer, R., et al. 2021. Implications of increasing household air conditioning use across the United States under a warming climate. Earth’s Future 10:e2021EF002434. Rattner, A. S., and S. Garimella. 2011. Energy harvesting, reuse, and upgrade to reduce primary energy usage in the U.S.A. Energy 36:6172–6183. Siddik, M. A. B., A. Shehabi, and L. Marston. 2021. The environmental footprint of data centers in the United States. Environmental Research Letters 16:064017.

Srinivas Garimella is the Hightower Chair in Engineering, a professor in the Woodruff School of Mechanical Engineering, and director of the Sustainable Thermal Systems Laboratory at the Georgia Institute of Technology. Matthew T. Hughes is a postdoctoral associate at the Massachusetts Institute of Technology. This article was adapted from a version previously published on The Conversation (theconversation.com). Email for Garimella: [email protected] 2023

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INTERNATIONAL FORUM ON RESEARCH EXCELLENCE

Featured Sessions Developing a culture of civic science through state-level policy engagement Adriana Banktson

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Infographic | Andy Brunning

DANDELIONS: DIURETICS AND RUBBER

DANDELIONS’ MEDICINAL USES

RUBBER FROM DANDELIONS

The French name for dandelion is pissenlit (“wet the bed”), which refers to the plant’s use in traditional medicine as a diuretic. Dandelions do contain several diuretic compounds, and limited studies in humans have confirmed their therapeutic efficacy. The plant’s high potassium content also helps replace potassium lost through urination.

The sticky white liquid that seeps from dandelion stems when they’re picked contains natural latex, which can be turned into rubber. The roots of Russian dandelions (Taraxacum kok-saghyz) contain a particularly high percentage of latex, making them ideal for rubber production.

potassium content of dandelion leaves versus bananas dandelion leaves

bananas

397 milligrams per 100 grams

358 milligrams per 100 grams

Source: U.S. Department of Agriculture FoodData Central

Dandelion extracts and compounds have anti-inflammatory, anticarcinogenic, and antioxidative properties. These effects are mostly due to polyphenols and sesquiterpenes, phytochemicals that are also responsible for the leaves’ bitter flavor. OH HO

O O

HO

O

H

O OH

Ci

332

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taraxinic acid β-D-glucopyranoside

sesquiterpene lactone in dandelions, also thought to be a contact allergen

1941 30% During World War II, nearly one-third of the USSR’s rubber was derived from the Russian dandelion to compensate for a shortage of natural rubber.

n cis-1,4-polyisoprene (main constituent of rubber)

In the past decade, tire manufacturers have developed dandelion-rubber tires. Bike tires made from this rubber are now commercially available, and manufacturers estimate that dandelion-rubber tires will be available for cars and trucks within the next 10 years.

© Andy Brunning/Compound Interest 2023 - www.compoundchem.com | @compoundchem Shared under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 license.

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First Person | Gabriel Reyes

In the past few years, there have been major initiatives to increase diversity, equity, and inclusion (DEI) in science and in the workforce. Yet the root causes of inequities are still being revealed. Neuroscience researchers are suggesting that poverty is a major player—noting that poverty is contributing to decreases in academic success, education level completed, and even brain mass. Gabriel Reyes, a PhD student in developmental and psychological sciences at Stanford University, is working at the heart of this subject. Reyes grew up in a low-income, underserved section of Albuquerque, New Mexico, where opportunities were limited. Nevertheless, his passion for neuroscience led him to attend Brown University, Columbia University, and now Stanford. He is the first in his family to graduate from college and is working at the intersection of DEI and neuroscience research. Reyes is also the founder of FLi Sci, a program that provides research opportunities to first-generation and low-income science students. Reyes attended Sigma Xi’s 2022 International Forum on Research Ethics (IFoRE), which focused on science convergence in an inclusive and diverse world, and spoke with Jordan Anderson, producer of American Scientist’s DEAIComSci podcast, about debunking poverty and educational inequity myths, and what current neuroscience research reveals about a path toward more equitable educational outcomes for students nationwide. (This interview has been edited for length and clarity.) What pressing issues in neuroscience does your research explore?

My research has two buckets. The first bucket is neuroscience and understanding how experiences and the environment affect our behavior. I had planned to understand how specific experiences influence decision-making. Two scientists who inspired me were Kim Noble and Bruce McCandliss, who are examining whether there is a correlation between poverty and academic achievement from a neuroscientific standpoint. Dr. Noble, at Columbia University, has written a lot of papers on poverty and brain development. Dr. McCandliss teaches at Stanford University and runs the Educational Neuroscience Initiative, using neuroscience to improve learning. Their work created a path for me to explore the associations between socioeconomic status and brain development and to theorize how that might translate into academic performance. But I didn’t get anywhere with that topic, because I was finding more research questions than insights. As I was learning more about the field, I began to realize that there are two problems. One is that how neuroscientists theorize and conceptualize poverty needs to be more consistent. For some people, poverty is defined by how much income your family makes. For another person, poverty might be defined by specific experiences communities endure. Are they able to pay www.americanscientist.org

rent on time? Are they in a lot of debt? Are they experiencing a lot of stress? This discrepancy is a conflict, because both definitions are related but are different constructs and therefore have different conclusions. The second issue was that we still need to fully understand fundamental learning mechanisms. How can

“We are looking at large datasets with a myriad of income analyses and thinking through how the story changes if you alter how you define poverty.” we speak to how people from lowincome versus high-income backgrounds learn, when we’re still figuring out how people generally learn? We are exploring how to bridge the two without problematizing the work. We want to avoid jumping to conclusions that have yet to be reached in neuroscience.

Courtesy of Gabriel Reyes

Poverty and Neuroscience

I want to start first by thinking about poverty as a construct. At Stanford, many of my projects interrogate how the field has measured poverty and whether we’re measuring it correctly. The most common index that I see these days is an income-to-needs ratio. And that is a federal poverty index, where officials define poverty by household income. However, for example, many neuro­ science studies need to consider that in New York City and the San Francisco Bay Area, rent is much higher on average than in rural Alabama. In rural places, $30,000 can take you much farther, but won’t get you very far in vast urban areas. That’s a massive issue for data analysis. Part of what I am now working on with Philip Fisher at Stanford is looking at large datasets with a myriad of income analyses and thinking through how the story changes if you alter how you define poverty. We want to explore the general theory of poverty in a way that speaks more to the environments that people experience. So that’s the second bucket of my research. You were exploring how poverty affects cognitive development with Dr. Noble. Can you give an example of how you are applying your previous neuroscience work to your current PhD research with Dr. Fisher, and how you are examining the definition of poverty?

Researchers such as Dr. Noble have found a particular association between looking at one’s socioeconomic status and the amount of cortical volume in particular individuals. Often, what they see is that there is a positive association between cortical volume and income. However, it is a nuanced ques2023

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tion, because cortical loss in higherincome communities does not mean equal or more significant cortical loss in people with lower socioeconomic status. Some studies don’t find that association. There are a lot of other variables, such as the research participant’s school and how socioeconomic status is measured. Researchers in this field are pushing toward different ways of understanding brain development, looking at nuanced ways of thinking through socioeconomic status. One of the ways is looking at experience with material deprivation or other factors beyond just the income-toneeds ratio to understand what happens with brain development. People who experience certain forms of economic adversities, such as food insecurity, are often more likely to have differences in cognitive function, cognitive behavior, and neural development. Some people don’t experience food insecurity but might be in the same income bracket. What sort of data are you exploring in your current research, and how is it affecting the field of neuroscience?

In my research, I analyzed data from the Fragile Families and Child Wellbeing Study. I was looking at various outcomes, one of which is working memory. That is an aspect of executive function—mental processes that enable us to plan, focus attention, remember, and juggle multiple tasks. It measures how much information people can hold at any given moment and is a typical topic in cognitive studies. It is also one where people often find things such as the association that people with lower income generally have lower working memory capacity than someone with higher income. And I used a friend’s framework for how we think about that to look at it through a different lens. So instead of just looking at the effect of income on performance, I wanted to see how people who experience more aspects of material deprivation behave throughout different income barriers. For example, someone who makes $10,000 and someone who makes $90,000 represent people in two separate income groups. But let’s say the person who earns $90,000 lives in a costly part of San Francisco and supports a family of eight. $90,000 may seem like a lot, but it doesn’t go that far when you think about how they’re using that money versus someone who is making $10,000 but is a single adult living somewhere like New Mexico. You can then ask questions 334

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nitive development. Higher levels of material deprivation can affect performance and working memory tasks for people across different income groups. We would not have found that association if it was just income alone. One of the things that we want to do is to see if we can measure qualitative rather than quantitative responses by creating written response questions on a massive survey database. By doing so, we can extract specific factors of the poverty experience that we can use to uncover a different way of categorizing family and community poverty without looking at income.

sures a behavioral outcome such as test scores. Based on prior studies, we might theorize that low-income people will have lower test scores than higher-income people. The problem is that this does not provide the root cause of what is happening. It also implies that low-income people are less capable than high-income people at standardized testing. This logic is not accurate. Even if those associations are occurring, income is not causing test performance. Instead, income might produce specific experiences in which higher-income people can score higher. Rather than asking people what their income is and dividing them by those groups, we can add a second variable that asks questions such as: Did you get access to private tutoring on the SAT or ACT? Did you attend a rigorous high school that provided resources to learn how to perform well on standardized testing? Now we have questions that might get to experiences contributing to test performance. If you add this dimension on top of income, we might find that, for example, low-income students who scored highly on the test had access to private tutoring or went to top-tier high schools. We may also find that lowincome students who performed poorly had none of these resources. This pattern also exists in middle-income groups and high-income groups. Neuroscience researchers are currently working on these insights, and we are building off of them. Applying that to the brain, we can see that there might be differences in cognitive performance and neural signatures when you only look at income, but we have started adding all these other measurements, such as: Are you experiencing high levels of threat? Are you experiencing high levels of food insecurity? Are you experiencing high levels of monetary scarcity? These new insights have created a differentiation between our knowledge of which part of the brain has specific patterns, which tells us that it’s not just income but rather experiences that income is either allowing or preventing some groups to have more often than others that are contributing to brain mass.

How has the research in your field changed over time?

How have your personal experiences influenced your choice of research?

like: Can you pay your rent on time? Did you make enough money to pay the electricity bill? Are you able to go to the hospital? Or did you not go to the hospital because you couldn’t afford the medical bill? We add up the number of those experiences and see that maybe someone who’s making $10,000 only had two moments of material deprivation for the questions we asked, but the person making $90,000 had nine of those moments out of 10. We want to see if there was an association between that sort of interaction effect with income and experiences of scarcity. My initial research found that income as a single variable is insufficient to understand how poverty affects cog-

“Instead of just looking at the effect of income on performance, I wanted to see how people who experience more aspects of material deprivation behave throughout different income barriers.”

Many studies have divided tasks or groups of people by low income, high income, or middle income. It could be a quick correlation task that mea-

I often had to turn down research opportunities that I knew would help me be a better scientist. I was poor, and I could not afford the opportunities. I would be

pushed away if I tried to advocate for financial assistance. In my undergraduate years, I had the chance to work on my thesis with a researcher I love, but I needed a lot of money to help my parents hire an immigration attorney. So instead, I worked for Google because they offered a larger salary. Two months as a full-time research assistant would barely pay rent. In my master’s program, a similar situation occurred where I could not afford to take the research assistant salary. So, I needed to figure out how to find a way to continue training as a researcher while managing my family’s financial circumstances. And the thing that galvanized me to create a program during my PhD that would allow me to support other students born into lowincome situations like myself was knowing that I could more easily have become a scientist if I only had had a little more financial support. Much of your neuroscience research is geared toward DEI. Are there other DEI spaces that you are involved in?

For many people who try to do scientific research, it is often hard to avoid diversity, equity, and inclusion efforts, because we often have to point out scientific injustices or champion for spac-

es for us to exist. So, on the one hand, I focused on poverty and development in psychology. On the other hand, I also do a lot of work in science education and diversity in science. One of

“We want to find the common factors that help people transition from an undergraduate experience to a tenuretrack profession.” the projects I am involved in is figuring out the antecedent to academic career success. We want to find the common factors that help people transition from an undergraduate experience to a tenure-track profession, especially for minoritized scientists. Another major project I am involved in is called FLi Sci. In the summer of 2020, every scientist talked about diver-

sity and inclusion in science. Implementing graduate mentorship programs was their number-one solution to provide more diversity efforts. Although these programs are important, scientists often pose them as the only solution. The root cause starts a lot sooner than college programs. I wanted to target high school students who went to lower-income schools, like I had, to prepare them earlier for college and graduate school. The goal was not to let lower-income students become college seniors lacking the research experience they needed to be competitive for PhD programs. Many students do not have enough experience to get postbaccalaureate opportunities, because it’s so competitive nowadays for people to get opportunities without a research background. So, I created FLi Sci because I was looking for other nonprofits targeting low-income or non–highachieving high school students. Often, these programs accepted previously accomplished students. They were students who did well on the PSAT or went to a magnet school. I struggled to find a program trying to recruit students without those opportunities. So, I decided to create it and see what would happen. 

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Briefings

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n this roundup, managing editor Stacey Lutkoski summarizes notable recent developments in scientific research, selected from reports compiled in the free electronic newsletter Sigma Xi SmartBrief: www​.smartbrief.com/sigmaxi/index.jsp

Neptune’s Cloudy Weather

ESO/P. Irwin et al.

For the first time, Earth-bound astronomers have peeked beneath the surface atmosphere of the Solar System’s mostdistant planet to understand the roots of its extreme and surprisingly dynamic weather. A team led by physicist Patrick G. J. Irwin of the University of Oxford used the European Southern Observatory’s Very Large Telescope (VLT) to capture images of a 10,000-kilometer-wide dark spot on Neptune’s northern hemisphere. They paired the VLT with a tool called the Multi-Unit Spectroscopic Explorer, or MUSE, which takes images at multiple wavelengths. Each wavelength probes at a different depth, and together they

create a composite 3D image. MUSE revealed that the dark spot is composed of icy, hazy air particles in a layer beneath the outer atmosphere. This finding rules out a previous theory that the dark spot is caused by clearing clouds. MUSE also uncovered something unexpected: a bright spot next to the dark spot. The bright spot is at the same depth as the dark spot but had not previously been identified, even by space-based telescopes, and appears to be a new type of cloud. The team’s discoveries using MUSE show new ways to use remote sensing from Earth to study the intense and complex weather systems on distant planets. Irwin, P. G. J., et al. Spectral determination of the colour and vertical structure of dark spots in Neptune’s atmosphere. Nature Astronomy doi:10.1038/s41550-023-02047-0 (August 24).

Mental Toll of School Closures Parents’ and educators’ anecdotal evidence of the psychological toll of school closures on children during the COVID-19 336

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pandemic now has the backing of data. Researchers led by economist Christina Felfe of the University of Konstanz in Germany used the German school system as a natural experiment to study the effects of school closures on children aged 11 to 17. They found that longer school closures correlated with worsening mental health measures, especially among boys, younger adolescents, and those living in close quarters. Each of the 16 German federal states manages their public schools independently, so although all of the states closed their schools between March 16 and March 18 of 2020, the reopening dates ranged from April 20 to June 15 of that year, and return-to-school strategies varied. The researchers merged information on school closures with mental health data collected by German national health surveys of 11- to 17-yearolds. They first compared responses from students at different grade levels in the same state to isolate any state-specific variables and then looked at students at the same grade level in different states to assess age-specific variations. The team found that each additional week of school closure was associated with a decrease in measures of the students’ health-related quality of life, and longer closures correlated to prolonged mental health disorders. These findings support the need for ongoing mental health services for school-age children and may help shape education policies in the case of a future pandemic. Felfe, C., et al. The youth mental health crisis: Quasi-experimental evidence on the role of school closures. Science Advances 9:eadh4030 (August 18).

Fire Ants Cross the Atlantic The invasive species Solenopsis invicta, commonly known as the red imported fire ant, has established a colony in Sicily, marking the first mature population in Europe. These insects threaten the local agriculture and ecosystems—a 2021 study in Nature ranked them as the fifth most costly invasive species—and their painful bites can cause severe allergic reactions in some people. A team of Spanish and Italian biologists documented 88 nests over 4.7 hectares in eastern Sicily. The species has reached Europe at least three other times but was intercepted before it could spread; however, the size and range of the Sicilian colonies mean that eradication is not likely to succeed. Approximately 7 percent of Europe cur-

rently has environmental conditions in which the ants would thrive; however, global climate change could extend the habitable area to 25 percent of the continent by 2050. Red imported fire ants are native to South America but have spread to Mexico, the United States, the Caribbean, Australia, and parts of Asia. They hitch rides on boats and plants and are also dispersed by the wind, which can carry queens on their flights to establish new colonies. Menchetti, M., et al. The invasive ant Solenopsis invicta is established in Europe. Current Biology 33:R879–R897 (September 11).

Uncovering Pompeii’s Slaves An addendum to the saying “History is written by the winners” might be “and by the elite,” because those groups have historically had the education to record their affairs and the money to buy objects that survive as artifacts. So the 2021 discovery of Roman slave quarters in the villa of Civita Giuliana outside Pompeii was a coup for historians, and new findings from the excavation add nuance to our understanding of slavery in the Roman Empire. Two rooms, preserved in ash from Mount Vesuvius’s eruption in 79 CE, provide a glimpse into the lives of their enslaved inhabitants. One room had three beds, one of which was short, perhaps for a child. The inhabitants slept on ropes tied into loose netting, similar to the design of many modern hammocks. The other room had a similar rope bed and also another, more comfortable bed that would have had a mattress. The archaeologists theorize that this bed may have belonged to a higher-status servant. Neither of the bedrooms nor the nearby stable had bars on the windows or locks on the doors to keep the slaves imprisoned, which suggests that the villa’s owners used other methods of control—the researchers suggest that the close quarters and the presence of the higher-status servant may have encouraged the slaves to police each other. Slavery was an important aspect of Roman society, but most accounts come from the perspective of the ruling class. These bedrooms inform historians’ understanding of how Roman slaves lived and the mechanisms for control slave­owners employed. Zuchtriegel, G., and C. A. Corbino. Of mice and men: New discoveries in the servants’ quarters of the Roman villa of Civita Giuliana near Pompeii. Scavi di Pompei 5 (August 20).

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Sightings

Uncovering Ancient Corrections

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he intricate and extensive murals that adorn the walls of ancient Egyptian tombs are no doubt masterful works of art, but their method of creation has long been thought of as having been a regimented production line rather than a free-flowing artistic process. Various levels of artisans were relegated to adding only their assigned layers to each of the illustrations, leaving little room for rethinking the approach. The style used to depict the poses, colors, and decorative elements of deities or others was also highly formalized, not left to the imagination of any particular artist. However, advances in imaging technology have now uncovered corrections and revisions to the tomb figures, bringing into question the accepted view of the process of these Egyptian artists millennia ago. Archaeologist Philippe Martinez of Sorbonne University in France and a large team of his colleagues describe how they revealed these alterations in the July 12 issue of the journal PLOS ONE. The researchers were examining the tomb chapels of high-ranking officials near the ancient city of Thebes (now Luxor) from what’s called the New Kingdom, which lasted from about 1549 to 1069 BCE, encompassing the 18th to 20th dynasties. “The walls of these shrines were often decorated, representing the dead in his dutiful life on Earth as well as his expectations for a bright future in the netherworld,” Martinez and his colleagues explain in their paper. Previously, the pigments used in these tomb scenes had been analyzed mostly by taking tiny samples back to laboratories. But the team of researchers had created a portable version of an imaging device that uses x-ray fluorescence to look at pigments, without contact or damage, while still in place in the tombs. The pigments used by ancient Egyptian artists are suitable for this type of imaging, because the different elements fluoresce at distinct wavelengths when they are bombarded with x-rays, and the rays can penetrate the top surface of paint to reveal other elements underneath. This portable x-ray fluorescence (pXRF) device is small enough to be checked luggage on an airplane, the team notes. The researchers became interested in focusing their work on artistic corrections when they were examining a known revision that had become slightly visible through the millennia-old wear and chemical reaction of paint, in the tomb chapel of Menna, an overseer under Amenhotep III, 1391–1353 BCE. The revision was made to the position of Menna’s arm, shown in a ritualized pose of adoring Osiris (see figures on opposite page). One surprise the team found was that the pigments used in the original and the corrected arms have

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different compositions, with the first version high in arsenic (common in realgar, a red pigment) and the revised version containing more iron (common in red ochre). That difference could mean that the correction was made by another artist at the same time using a separate batch of pigment, or that the change happened later. The purpose of the rather small position adjustment remains unclear, however. The second tomb chapel the team examined belonged to Nakhtamun, chief of the altar in the Ramesseum temple, in about 1100 BCE. Because this tomb features a portrait of Ramesses II, it has usually been dated to his reign. However, some inconsistencies with standard Egyptian iconography, including beard stubble and an Adam’s apple, inspired Martinez and his team to take a closer look. Their pXRF showed signatures of copper, characteristic of the pigments Egyptian blue and green, even though these colors are barely visible now. Another hidden detail they revealed was that the original scepter (called a heka) appears to have been wider and to have obscured part of the chin. Indeed, the portrait seems to have had all its pharaonic insignia retouched: The crown (or khepresh) and necklace (or wesekh) originally had quite different shapes. Martinez and his colleagues note that the original depiction more closely resembles a necklace style called a shebyu, which was common in royal portraits from the 20th dynasty, after the death of Ramesses II. The team speculates that this change could indicate that the tomb dates later than originally thought, after Ramesses II had become deified, and that the original depiction had been recognized to be anachronistic and was thus repainted. “A lot of this modern and theoretical reconstruction is, however, based on the usual archaeological guessing game that aims at filling the remaining blanks,” Martinez and the team say. “We remain clearly ignorant of what was really important and significant for the ancient Egyptian eye and mind.” As was the case with the team’s imaging of the trace remnants of Egyptian blue and green, this pXRF method could also have the potential to help with reconstructing areas of these ancient tombs that have been damaged or weathered to the point that their murals are no longer visible, but which might retain pigment residues that could still be detectable. The researchers also hope to undertake a more systematic inspection of other tomb murals to try to characterize how common corrections were. “Due to the fact that most of the scientific inspections of these works of art have been carried out only through direct visual observation,” they say, “this may very well be but the tip of the iceberg.” —Fenella Saunders

Top and bottom from P. Martinez et al., PLOS ONE 18(7):e0287647. Middle: M. Alfeld et al., Comptes Redus Physique 19:625.

Pigment fluorescence reveals artistic revisions beneath Egyptian tomb murals.

A portable x-ray fluorescence (pXRF) device set up in an ancient Egyptian tomb chapel (right) is able to reveal pigments beneath a mural’s surface layer, because different pigments fluoresce at distinct wavelengths when bombarded with x-rays. In this mural, the arm of the official Menna was altered from its original pose. The correction is slightly visible now (A, below) because of paint wear and chemical reactions over millennia. The change shows up more clearly under ultraviolet light (B). Details of the correction (C and D) show pigment interactions. The original arm pigment contained more arsenic (As, in E), and the correction was higher in iron (Fe); the two also show differences in calcium (Ca), sulfur (S), titanium (Ti), and strontium (Sr). In another tomb (above), a depiction of Ramesses II shows changes in the shape of the necklace, crown, and staff, as is made visible by pXRF imaging of copper (Cu), arsenic, and iron (green lines show earlier version, red lines show correction, and blue lines show original shape of this style of crown, called a khepresh).

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Perspective

(Don’t) Shut Your π-Hole Like charges repel and opposite charges attract. That law of physics dominates organic chemistry and our everyday lives—and causes feuds among chemists. Dean J. Tantillo

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ttractions and repulsions form the basis of chemistry, including the biochemistry that allows our cells to function and the organic chemistry that enables much of the modern chemical industry. If you want to know how a new drug will interact with a disease-causing protein, or if you want to investigate the ways that cells build their internal structures, you ultimately need to examine the pushes and pulls between electrical charges. That sounds simple, but like everything in nature, simple concepts turn really hairy when you dig down into the details. Even though most molecules are not charged overall, they have regions that are more negatively or positively charged—places that naturally want to balance their situation by interacting with an oppositely charged part of another molecule. That hunger for balance is the basis of most chemical interactions, leading molecules to point their electron-rich parts at the electrondeficient parts of other molecules. For example, organic chemists commonly talk about an electron-rich group, or nucleophile, approaching an electronpoor carbon atom within a carbonyl (carbon double-bonded to oxygen) group and “attacking” it to form a new bond. Carbonyl groups are present in many important biomolecules such as sugars, lipids, and peptides,

so such reactions are key to life. These reactions help amino acids assemble to form proteins, such as collagen, and allow cells to digest proteins when they are no longer needed. Chemists have discussed carbonyl chemistry for approximately a century, but a relatively new term has arisen to

Dean Tantillo

When covalent bonds form, electrons are shared, often unequally, across multiple atoms, resulting in regions of positive and negative charge even in molecules that are neutral overall. Chemists create electron density maps to visualize these patterns known as σ-holes and π-holes. In the example above, blue regions have greater negative charge, red areas have more positive charge, and green and yellow areas have intermediate charge. Selenium fluorobromide (lower left) has a σ-hole. Sulfur trioxide (top) and chlorofluorotetrazole (bottom right) both have π-holes.

describe the electron-deficient property of carbonyls and other similar bonds: the π-hole. Organic molecules are held together by bonds that share electrons, but chemists don’t think of electrons simply as particles or points. Instead, they describe them as smears of charge between atoms, a concept known as electron density. There are two primary types of these electron-sharing bonds: σ and π (sigma and pi). In a σ-bond, most of the electron density associated with the bond is distributed around a direct line between the two neighboring nuclei. In π-bonding, the electron density resides either above or below the atoms but not in the sandwich region connecting them. Different types of atoms in a bond don’t share electron density evenly. And when one of the atoms in a π-bond draws a disproportionate share of the electron density toward it, such as oxygen in a carbonyl group, the carbon atom sports a π-hole—a region of positive charge found in the clouds that make up the bread of the electron-density sandwich of the π-bond. For example, the structure of collagen—the most abundant protein in mammals, found in skin, cartilage, tendons, and ligaments—contains many carbonyl groups and therefore many π-holes. If you want to understand collagen, you need to know what those π-holes are doing.

QUICK TAKE Differing molecules have varying amounts of positive and negative charge across their surfaces, and that variation affects their shapes and reactions.

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σ-holes and π-holes both present an area of positive charge on a molecule’s surface, which can help researchers predict the particle’s behavior.

Debate among chemists studying these interactions can lead to advances that fuel the design of new drugs and materials based on these patterns.

Steve Gschmeissner/Science Source

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Intertwined bundles of collagen provide structure to connective tissues that surround individual nerve fibers, as seen in this micrograph (above). π-holes help determine the structure of collagen and many other proteins. Collagen is formed from protein helices (below) that wrap around one another like analog telephone cords. Each helix is stabilized by π-hole interactions.

shown—corresponding to positive charge—near the carbon of the carbonyl group in each unit of collagen. This charge variation has implications

for molecular shape. In collagen’s 3D structure, for instance, three peptide strands coil around one another like analog telephone cords, with each

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MOLEKUUL/Science Source

Chemists visualize the positively and negatively charged regions that a molecule presents along its exterior by computing electrostatic potential surfaces, wrapping the molecule in a brightly colored sleeve that shows regions of positive (blue) and negative (red) charge, including π-holes. In the figure at the bottom of page 342, blue is

σ and π Bonding Charged surfaces are one way that chemists rationalize how a molecule’s electrons shape its behavior. But chemists also think about orbitals, which are mathematical functions related to the probability of finding electrons in particular locations. In this concept, when two orbitals interact, they form two new orbitals that distribute the electrons more, resulting in one orbital that is lower in energy than the energy of either starting atomic orbital, and one that is higher. For all molecules discussed in this article, only two electrons are involved in these interactions, and these electrons both get to “reside” in the lower energy orbital, or bonding orbital, that results from the interaction. The higher-energy, more-delocalized orbital that results from the interaction is called the antibonding orbital, and because it is “empty”—no electrons reside in it—it does not hurt the energy of the molecule. б-bonding

π-bonding

Collagen, the most abundant protein in mammals, contains many π-holes. If you want to understand collagen, you need to know what those π-holes are doing.

antibonding

energy

antibonding

bonding bonding Dean Tantillo

individual strand forming a helix because the electron-rich carbonyl oxygen from one amide (N – C = O) is attracted to the π-hole of another amide carbonyl further down the strand. With such maps, it sounds straightforward to predict how molecules

should interact, but chemists argue about the nature of π-hole binding. The nature of intermolecular interactions is a long-standing issue in physical chemistry, but the focus on holes is a modern one. The plots of many π-hole surfaces show a lot of blue, suggest-

favorable interaction

π-hole Dean Tantillo

This atomic-scale view of a peptide chain shows how an electron-rich oxygen from one amide group interacts with an electron-poor carbon from another further down the strand. These types of π-hole interactions stabilize protein helices, such as those within collagen. 342

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ing that many regions of the molecule could be attracted to an electron-rich partner. Some argue that the region of positive electrostatic potential near a carbonyl shouldn’t be considered a localized hole. And in some molecules, unambiguous holes in the electron density aren’t actually attracted to electron-rich groups. Getting to the bottom of these details might sound esoteric, but it is important for understanding how molecules are put together. It also has practical implications: If chemists understand how π-holes work, they

can do a better job of predicting the outcomes of chemical reactions and designing new ones in areas from biology to industry. Digging into π-Holes These unusual patterns of charge have inspired chemists to look deeply into the origins of the stabilization associated with π-hole interactions. Not surprisingly, deep dives have led to passion-filled debates. What are the bases of the arguments? First and foremost, electron density in a molecule is inherently spread out, albeit unequally, across the whole molecule, but chemists tend to want to carve it into chunks, in part because we have been trained to think of molecules as assemblies of functional parts. But electron density doesn’t come in parts, so fragmenting it, while potentially useful, cannot be done in a single correct way. There is no consensus, and arguments, sometimes ferocious, about which fragments make the most sense, ensue. Second, chemists frequently disagree about which physical factors contributing to attraction are most important. So far, we’ve talked about charge–charge attraction as being im-

portant for holding collagen together. But another way to look at this question is through molecular orbital interactions. Molecular orbitals are another way to describe the electron smears within bonds—instead of defining them simply as volumes of charge, orbitals are wavelike mathematical functions describing the probability that an electron resides in a particular area. Electrons can act like waves as well as particles, which means that they can interfere with each other as they interact, both constructively and destructively. Constructive interference equals favorable molecular orbital interactions. Sometimes, the chemists involved only have eyes for their favorite contributors to bonding and binding. As one leader in the theoretical characterization of such interactions, the University of Richmond’s Kelling Donald, says, they are feeling different parts of the same proverbial elephant without taking in the whole beast. Still, sometimes being focused can be useful. Ron Raines’s group at the Massachusetts Institute of Technology (MIT) has demonstrated through elegant laboratory and theoretical experiments that the interactions between amide groups described previously stabilize

Even if chemists arrive at different models of how π-hole and σ-hole interactions work, these models can lead to testable predictions and drive new experiments. the 3D structure of collagen. Their description of π-hole binding is mostly based on favorable molecular orbital interactions, rather than on the chargebased model. Which is correct? Based on my experience, I would say that both effects contribute. And focusing on either aspect can be useful. For example, the Raines group and Mohammad Movassaghi’s group, also at MIT, have applied what they’ve learned about π-holes to aid drug design, putwww.americanscientist.org

cobimetinib

б-hole F

F

N H

N HO

I

HN O

Dean Tantillo

F

Cobimetinib—an anticancer drug—includes a bond (circled) between a benzene ring and an iodine atom. This bonding arrangement creates a σ-hole, an area of positive charge (blue bull’s-eye) in this electron density map.

ting their orbital analysis of π-holes to use to tweak the structures of anticancer drugs so that they are more likely to remain stable in the body without losing their effectiveness. Studying σ-holes Like their π-hole cousins, σ-holes spark both arguments and opportunities for chemical innovation. Within a σ-hole, a region of positive charge is found along the line connecting two covalently bonded atoms, but not between the atoms, as in another anticancer drug called cobimetinib, used to treat certain types of melanoma. Chemists have recognized the potential role of σ-holes in a range of binding patterns. They can determine the local preferred shapes of single molecules. They can help small molecules bind to large ones. They can hold molecules together in repeating patterns in crystals and liquid crystals. The poster children of σ-hole–­containing molecules are the so-called aryl halides like cobimetinib—­ molecules in which halogen atoms, such as chlorine, bromine, and iodine, are attached to benzene (or related) rings. In x-ray crystal structures, such molecules often interact by pointing their carbon–halogen bonds at ­electron-rich atoms in other molecules.

This type of σ-hole interaction has its own name: halogen bonding. In the context of medicinal chemistry, electrostatic potential surfaces can be thought of as what a protein binding site “sees” when confronted with a drug. If the drug is a good match for the binding site, the binding site will look like a negative of this surface—a cavity of approximately the same size and shape whose surface charge distribution is opposite to that in the drug molecule. Cobimetinib offers a classic example of how a σ-hole within a drug molecule can facilitate that beneficial interaction, allowing it to bind to its target, a protein involved in the rapid proliferation of malignant cells. The same arguments that arise over the origins of π-hole interactions also surface for σ-hole interactions, and for the same reasons: As much as we understand about the basic attractions and repulsions that drive chemistry, we still have much to learn about the subtle ways that electrons and charges control the shapes and reactivity of complex molecules. Even if different chemists arrive at different models of how π-hole and σ-hole interactions work, these models can be useful if they lead to testable predictions and drive new experiments that shape molecular and materials design. 2023

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complex that assembles into a liquid crystal

N

I halogen bond

б-hole

electron-rich group

cationic intermediate in an organocatalyzed reaction

x:

Dean Tantillo

Interactions that include σ-holes can stabilize both long-lasting and transient chemical structures. An electron-rich pyridine group (that includes the N above) interacts with the σ-hole of an aryl halide in a complex that assembles into a liquid crystal. Electron-rich groups (lower image) can interact with σ-holes in a reactive intermediate, a short-lived structure within a chemical reaction that determines a product’s composition, connectivity, and shape.

As Bernard Silvi from Sorbonne University in France wrote in a 2019 paper, “The origin of this dispersion of opinions is not a crisis of our discipline announcing the advent of a new paradigm but rather a consequence of its good health.  .  .  . These systems of explanation .  .  . address different meanings of a given question and are intended for different scientific (sub)communities. Each system corresponds to its own representation of the microscopic matter, adopts its own point of view, and uses its own vocabulary.” Luckily, multiple viewpoints tend to spark future experiments, which should fuel better predictions about how changing molecules’ electronic structure will affect the strengths of their interactions. For example, both π-hole and σ-hole interactions have become part of the medicinal chemist’s toolbox for rational drug design: the process of building new molecules that can counteract the effects of disease-causing proteins. As chemists catalog the geometries of 344

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interactions such as π-hole and σ-hole interactions through x-ray crystal structures of small molecules binding to proteins, they can predict the best orientations of the two partners participating in those interactions and attempt to understand the origins of their attraction using quantum mechanics calculations. But using what they learn from those quantum mechanics calculations (whether they reach a consensus or not), chemists can then derive simple mathematical equations that they can employ to rapidly predict how new, smallmolecule drugs might bind to a target protein’s binding site. These strategies now propel molecular design of new drugs for diseases ranging from HIV to cancer that bind via σ-hole interactions, new polymers that hold themselves together using π-hole interactions, and more. Regarding this problem from multiple viewpoints, learning from each, and applying those lessons has helped chemists design new molecules and new experiments. So let’s hope the

c ontinues—let’s keep discussion ­ those pie holes open. References Andrés, J., et al. 2019. Nine questions on energy decomposition analysis. Journal of Computational Chemistry 40:2248–2283. Berger, G., P. Frangville, and F. Meyer. 2020. Halogen bonding for molecular recognition: New developments in materials and biological sciences. Chemical Communications 56:4970–4981. Kilgore, H. R., C. R. Olsson, K. A. D’Angelo, M. Movassaghi, and R. T. Raines. 2020. n→π* interactions modulate the disulfide reduction potential of epidithiodiketopiperazines. Journal of the American Chemical Society 142:15107–15115. Naaz, S., et al. 2022. Halogen···halogen and π-Hole interactions in supramolecular aggregates and electrical conductivity properties of Cu(II)-based 1D coordination polymers. Crystal Growth & Design 22:5189–5197. Newberry, R. W., and R. T. Raines. 2017. The n→π* interaction. Accounts of Chemical Research 50:1838–1846. Wilcken, R., M. O. Zimmermann, A. Lange,­A. C. Joerger, and F. M. Boeckler. 2013. Principles and applications of halogen bonding in medicinal chemistry and chemical biology. Journal of Medicinal Chemistry 56:1363–1388.

Dean Tantillo loves to study the complexity associated with his young children and with the mechanisms of chemical reactions. He does both in Northern California, where he is a professor of chemistry at the University of California, Davis. Email: [email protected]

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Technologue

How Herman Hollerith Counted America and the World In the late 1800s, the inventor designed a revolutionary punch-card tabulating system, a key moment in the development of modern computing. Ainissa Ramirez

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n 1879, 19-year-old Herman Hollerith aimed to make a name for himself and wash off the stain of New York City poverty. His father had died when he was about 10. The tragedy not only shook his family to the core, but it also forced them to leave the comfort of their tight-knit enclave of German relatives in Buffalo, New York. It was there that his mother began making one-of-a-kind bonnets for sophisticated ladies. But after she was widowed, she became a full-time milliner. She moved her family to New York City, where she could reach more customers. Herman was a sensitive boy, and the transition to New York City seemed to impact him deeply. When a spelling bee was announced at school, he jumped out of his classroom’s second story window, choosing bodily harm over revealing his weakness in spelling. Fortunately, his astute mother recognized her youngest child’s acrobatics as a call for help and hired a Lutheran minister to provide private tutoring. Under the clergy member’s instruction, Herman’s genius soared. He entered the Columbia University School of Mines at the age of 16, studying metals and mining. When he graduated with his Engineer of Mines degree in 1879, he posed for a photograph (see figure at right), donning an extravagant top hat and coat on his thin, barely six-foot-tall frame. His task now was to find work to match his ambition.

With a knowledge of metallurgy from his engineering degree, Hollerith landed a job as a Special Agent at the U.S. Census Office in Washington, D.C., writing reports on the use of

Library of Congress Prints and Photographs Division

In 1879, 19-year-old Herman Hollerith graduated from the Columbia University School of Mines. He soon landed a job writing reports at the U.S. Census Office, unaware of how it would influence the rest of his career.

water and steam power for iron- and steel-making. While at the Census Office, he also discovered that the United States government did not have a full

idea about the granular makeup of its citizens. Additionally, Hollerith realized that the way the Census clerks scribbled numbers on paper seemed barely more advanced than Babylonian hatch marks in clay. He also watched as mountains of census forms were tallied by hand, taking up most of the decade and threatening to overlap with the following count. One evening at a party, Hollerith connected with one of the most prominent men working on the 1880 Census—John Shaw Billings, an esteemed physician and Army surgeon, who had created an unrivaled medical library and was in charge of the 5th Division of the Census on Vital Statistics. Hollerith admired Billings greatly, doing extra work for him by compiling life tables and graphs, in addition to the reports Hollerith already had to write. Sometime around 1879, Billings invited Hollerith over for tea. On that Sunday evening, the older man waxed poetic about the technology the Census needed. Billings had long been dissatisfied with how the Census was conducted and had been collecting information about individuals by storing key details on cards with well-placed small holes to mark information. Looking at the young and motivated Hollerith, Billings said, “There ought to be a machine to help tally all this information.” Such an invention would

QUICK TAKE The 1880 U.S. Census took seven years to complete. Seeing this glacial pace, a young, ambitious Herman Hollerith working at the Census Office began brainstorming solutions.

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Hollerith’s tabulating system used punch cards run through an electrical machine that compiled the data. A rough count for the 1890 Census was completed in six weeks.

Hollerith’s tabulators were used to compile all sorts of data around the world for several decades. His company eventually merged with others to form IBM.

Division of Medicine and Science, National Museum of American History, Smithsonian Institution

Hollerith invented a set of machines for compiling data for the U.S. Census. The system included a punch machine (left) for entering data about each person onto a blank card, a tabulator (center) for reading the cards, and a file box for sorting the cards (right). When a punched card was inserted into the metal contraption on the right side of the tabulator and the crank was pulled, it would complete a circuit and count the data points on the dials above the tabulator. This concept of punch-card tabulating would make its way later into modern computing.

undoubtedly change how quickly the Census was counted, as well as save the government millions of dollars. In that moment, Billings planted a seed in the fertile soil of Hollerith’s mind. Getting to the Punch Hollerith feverishly investigated how a tabulating machine might function, learning more about the Census’s operation by taking on additional work in another part of the organization. After becoming knowledgeable about the current processes, Hollerith started to hatch an idea that he was excited to share with Billings. However, when Hollerith explained his new scheme, Billings wasn’t interested in working with him to develop a machine. Billings just wanted the ready-made solution. Disappointed but not discouraged, Hollerith set off to explore how www.americanscientist.org

to count the entire U.S. population with a machine of his own design. Hollerith learned all he could about one machine that had been used in the previous Census. Prior to that Census, clerks had tabulated by hand on tallying sheets. In 1872, Charles Seaton created a machine that looks like a modern-day pasta maker. Each ribbon of paper that was spit out was a tally sheet that pertained to a specific column of demographic data. The paper could then be advanced to a blank region, ready to receive new data. This invention was a step in the right direction, but it had many limitations, because it was essentially a compact tally sheet. Hollerith understood that a new machine was needed that not only collected data but also counted it. To better understand this earlier invention, Hollerith spent all his free time

in Washington soaking up as much as he could from Seaton. But soon Hollerith’s appointment at the Census Office came to an end. He tried to find another job nearby. The best position he could find that gave him the freedom to tinker was a teaching position at the Massachusetts Institute of Technology (MIT). Most young men would be thrilled to be affiliated with such an institution, but Hollerith wasn’t entirely convinced. He was reluctant to accept a pay cut. But after a former teacher from Columbia reminded him that one’s salary was no measure of one’s value, Hollerith took the job. Although his body was located in Boston (MIT’s home before Cambridge), his mind never left Washington, D.C. While teaching mechanical engineering at MIT, 24-year-old Hollerith spent all his free time working on his “Census Machine.” His first attempt in 1882 used a strip of paper, like Seaton’s device, with a hand punch and a reader. Holes were punched into the paper. A hole was registered in the reader by a pin hovering over its metal roller. When electronic contact was made, the 2023

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The Art Institute of Chicago, Art Resource, NY

hole would be counted. But model, but the machine wasn’t soon the shortcoming of this quite ready for full-scale use. approach became obvious. To get the invention where he With information stored this needed it to be, Hollerith reway, it was difficult to get quired money to build a robust to a specific file without unversion as well as funds for the raveling the whole roll. Plus, patent filing fee. This plan felt Hollerith found that it took foolproof to him, which is why what felt like miles of continhe pleaded for additional funduous paper to store informaing from Meyer, imploring to tion about just a few people. his brother-­in-law in a letter He began to think there had that he was no longer workto be another way to store ining on a “crude machine.” But formation compactly and acMeyer wasn’t convinced, and cess it readily. Soon, his ideas the money never came. When moved away from using long Hollerith asked other family strips of paper with holes to members for funding, legend using cards with punched has it that they laughed. Desholes—a concept that dated perate, Hollerith attempted back to his days at university. to find other ways to come When Hollerith had atup with the money. He soon tended Columbia, he lived looked toward the railroads. with his older sister Bertha Since the end of the Civil Meyer and her husband AlWar in 1865, the amount of bert. Albert worked in the railroad track in the United silk industry and tried his States had been growing rapbest to convince his young idly, and the railroads were ward to join him in textiles. becoming America’s biggest Hollerith had a strong me- Hollerith came up with the idea of using punch cards to tally cen- industry, guaranteeing a pot chanical sense, and the textile sus data after becoming familiar with their use in textile looms. of gold for any inventor who industry had many opportu- The miniature model above includes a Jacquard attachment at the could create a useful technolonities that might have suited top, which used a series of punch cards to program each thread in- gy for trains. Hollerith combed him. But he also loved the dividually. This system could replicate complex weaving patterns. through railroad journals seekpractical uses of science, such ing opportunities to build as the chemistry of beer, about which writing a successful patent, so he de- something, and he found that there he presented for the Chemical Society cided to get a position at the U.S. Pat- was a competition in Iowa hosted by while still a student at Columbia in ent Office. Then, after about two years, the Master Car Builders, scheduled for 1878. Textiles did not fully align with he quit and worked for himself as an 1887. The contest involved designing Hollerith’s temperament, so he didn’t “Expert and Solicitor of Patents,” as- a better braking system. At that time, take up his brother-in-law on the offer. sisting other inventors with writing brakes were crude, and many passenBut Hollerith saw something in the these legal documents for a fee. gers feared bodily harm even riding textile factory that never left him. trains. With nothing to lose, Hollerith One day, Meyer showed young Holtossed his hat in the ring. lerith a special loom that created comFive brake systems were tested in plex pictures and lace designs, getting the competition: three using comdirections from punch cards. Decades pressed air, one using vacuum, and earlier in the 1800s, Joseph Marie JacHollerith’s using electric brakes. Holquard had invented this loom in France. lerith designed this electricity-based The holes in the cards allowed long brake system at a time when Thomas weaving hooks to pass, creating an Edison was bringing incandescent image line by line. Where holes were bulbs to the world. Hollerith won in absent, stitches were not made. These the competition but he also lost. His Jacquard looms were all over France train stopped three seconds faster and and had migrated to Europe and later to 128 feet (39 meters) sooner than the the United States. Years later, Hollerith air brakes. Also, his system didn’t jolt would realize that the way these cards From Concept to Prototype passengers. But in the end, the judgstored information for weaving might Hollerith continued to tinker on his in- es were uncertain about how electric vention and ended up spending all of brakes would operate during a thunalso store information for the Census. In 1883, Hollerith left MIT and re- his income on his creation. When he derstorm, not to mention that many turned to Washington, D.C., to find wasn’t working on it, he was meeting superstitions still existed about electricwork. As he continued work on his officials at the Census Office, reporting ity. So the judges gave the prize to the “Census Machine,” he realized he on his progress to them. One day, these air brake system made by a popular needed to know everything about officials invited him to demonstrate his inventor named George Westinghouse,

Hollerith designed an electricity-based brake system at a time when Thomas Edison was bringing incandescent bulbs to the world.

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who already had a number of inventions in service in the railroad industry. This loss stung Hollerith deeply, and, according to his biographer Geoffrey Austrian, he barred people around him from mentioning the name “Westinghouse.” But Hollerith’s luck would soon turn around. The City of Baltimore was desperate to efficiently collect their mortality statistics (such as causes of death) and contacted Hollerith, probably after hearing about his work from Billings. In 1887, this city that birthed America’s national anthem also ushered in a new age of data by using Hollerith’s punch-card tabulating machine to acquire information about its citizens—both the quick and the dead. When collecting such information, Hollerith used cards inspired by train tickets, where a conductor punched holes describing the rider, such as light hair, dark eyes, or long nose. These “punch photographs” helped identify and verify passengers. Hollerith initially used a conductor’s punch, too, but after perforating 1,000 cards in one day, each with multiple holes, his arm was too sore for a repeat performance. These aches and pains inspired him to devise a machine with a lever inside to punch the cards; like a seesaw with a well-placed fulcrum, it required much less force on the hand. Hollerith succeeded in Baltimore, and soon other opportunities materialized. www.americanscientist.org

Hollerith’s tabulating system came to be used in censuses around the world. For example, this punch card was used in the Philippine Census of 1903.

The health departments of New Jersey and New York City sought his services and had both adopted his system by 1889. Hollerith’s system was able to tabulate health-related statistics in a frac-

tion of the time that the task took by hand, which was a great achievement. But his eyes were still set on the Everest of data he wanted to conquer—the next U.S. Census, happening in 1890.

NARA/Science Source

An operator reads census forms and punches holes into dollar-bill-sized cards in a pattern that represents the data. 2023

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Hollerith’s invention was featured on the cover of Scientific American on August 30, 1890. Illustrations show various steps in the census tallying process. The previous year, Hollerith’s tabulator had won a gold medal at the World’s Fair in Paris.

Speeding Up the Census Until 1880, counting the number of citizens in the United States happened at a glacial pace. There were 26 questions on the 1880 Census, which captured information such as gender, place of birth, race, marital status, occupation, ability to read or write, and disability status. But there was no way to sift or sort all that data to know the number of persons in any combination of the categories. Hollerith designed an en350

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tire punch-card system that allowed the Census to not only count the total population, but also to separate them into smaller demographic groups, providing the nation with a mirror to know itself. At the time that Hollerith was working on his system, other inventors were coming up with their own solutions. The Census Office had a competition of statistical machines, in which three competitors compiled data of

10,491 people living in four districts of St. Louis, Missouri. One system made by William C. Hunt recorded information about each person on slips of paper that were counted by hand; another system by Charles F. Pidgin was a modification of the first, using different colored paper, called chips, that were also sorted and counted by hand. This time, Hollerith was the competition’s clear winner. Neither of these manual methods of slips or chips could keep up with Hollerith’s machine, which worked in nearly half the time to translate the data onto cards, and one-tenth of the time to tabulate the information. The 1890 Census and Beyond When the U.S. Census of 1890 began, Hollerith’s moment had finally come. Now 30 years old, Hollerith saw his automated tabulating punch-card system fully actualized. First, Census employees traveled door-to-door, taking down details about members of a household. Armed with forms containing nearly 30 questions, they scribbled down the information or in some cases directly punched that information onto a card. If a mistake was made on a card, the hole was patched with a small adhesive cover. Literal tons of paper forms were then returned to the Census Office, where the data were translated into holes punched into cards, with a keyboard that neatly pierced them, readying the card to be counted. Next, the information on the card was tallied by a clerk sitting at the tabulation machine, which resembled an upright piano with counters distributed in rows and columns on its upper panel. At the location of the piano keys sat a small press, which looked like a square waffle iron with a medieval bed of nails coming from the top. If the nail passed through a hole in the card when the clerk pressed down, the nail completed an electrical circuit, sending current to a specific electronic counter. The counters looked like clocks, but instead of 60 minutes, they had 100 divisions. A long hand, like the minute hand, moved one division to count “one.” The shorter hand, like the hour hand, moved one division to count “hundreds.” If the nail did not pass through a hole in the card, the counter didn’t move. After each card, the clerk lifted up the press, ready to count the next. Stacks of cards as high as the Washington Monument were tabulated every day.

U. S. National Archives Records Administration

The 1880 Census, conducted before Hollerith’s invention, had taken nearly seven and a half years to complete. In 1890, a rough count of the entire U.S. population was performed twice in six weeks. According to the current Census historian, it took approximately two to three years to fully process and tabulate all the various Census subjects. Soon, other countries came clamoring for this technology. Hollerith applied his automated census machines to counting populations in Austria, Canada, Russia, Cuba, Puerto Rico,

The 1880 Census, before Hollerith’s invention, had taken nearly seven and a half years to complete. and Norway. The results allowed these countries to get a clearer picture of themselves, too. In 1890, the same year as his Census triumph, Hollerith received a doctorate from Columbia for his electric tabulating system. By 1896, he formed www.americanscientist.org

Hollerith’s tabulating machine changed the way populations were counted. The census was not only a way for the country to know itself, it also reflected the times. Employment in the federal government was segregated until 1947. This photograph from the 1940s shows African American punch-card operators from the Census Office. They were part of the workforce of 2,400 punch-card operators that entered 328,341,293 cards for the census.

the Tabulating Machine Company and would go on to secure a contract for the 1900 Census. The Census of 1910 also seemed like a sure deal, but the Census Office didn’t want to pay Hollerith’s fees. One of Hollerith’s former employees quickly seized this opportunity by using Hollerith’s plans to make his own machines. Hollerith knew this employee well, having given him loans to buy a home and to help him with the care of a sick child. The betrayal cut deeply, but it forced Hollerith to look into new markets and provide new services for businesses and industry, such as accounting, recordkeeping, and statistical analysis. Soon, Hollerith had other customers, such as George Westinghouse (a name he had once vowed never to utter) and the Marshall Field’s department store, as well as electric companies, insurance companies, steel manufacturers, and railroads. Later, Hollerith’s business would merge to form a new entity called the Computing-­Tabulating-Recording Company (C-T-R). That company was

eventually folded into a newly formed company, called International Business Machines (IBM), bringing Hollerith’s punch cards—and a new way to store data—to every corner of the world. Bibliography Austrian, G. D. 1982. Herman Hollerith: Forgotten Giant of Information Processing. New York: Columbia University Press. Blodgett, J. H., and C. K. Schultz. 1969. Herman Hollerith: Data processing pioneer. American Documentation 20:221–226. Hollerith, V., and H. Hollerith. 1971. Biographical sketch of Herman Hollerith. Isis 62:69–78. Reid-Green, K. S. 1989. The history of census tabulation. Scientific American 260:98–103.

Ainissa Ramirez is a materials scientist who began her career as a Member of Technical Staff at Bell Laboratories and was later an associate professor of mechanical engineering at Yale University. She is the author of the award-winning book The Alchemy of Us (MIT Press, 2020). Currently, she is a Kluge Scholar at the Library of Congress and is working on her next book about material science innovations throughout history. Website: www.ainissaramirez.com 2023

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“Seeing” into Opaque Materials with Light and Sound Lasers generate and detect ultrasonic waves that can image the interiors of solid objects. David M. Pepper and Todd W. Murray

P

eople have always been fascinated by things that are hidden from view, and by what might be found inside opaque objects. We see objects because some of the light that strikes them is reflected and eventually enters our eyes. However, not all of the light is reflected from the surface; part of it is absorbed. Is there anything useful that can be done with this absorbed light to see within the object? The answer lies in a serendipitous observation made more than 140 years ago by Alexander Graham Bell when he heard sounds produced by light falling on an opaque object. Bell was working on one of his more intriguing inventions, the photophone. It used sunlight, instead of wires, to carry voice information between two individuals. The sunlight was modulated by the voice of the speaker and was converted to electrical signals at the other end with a detector made from selenium. This invention was similar in principle to today’s fiber-optic communication, except that Bell did not confine the light to a fiber. In the process of his experimentation with the photophone, Bell discovered that it was possible to hear the sound by simply placing his ear in the air close to an object that was illuminated by the light—no electri-

cal connections were necessary. What Bell heard was the result of the formation of sound waves by the rapid thermal expansion and contraction of the air over the periodically heated surface, which is now referred to as the photoacoustic effect. His observation was the basis for a novel technology using lasers that now enables us to see into the interiors of opaque objects without ever ­touching them.

surface of a solid, the result is the generation of heat-induced surface temperature changes, leading to pressuredensity waves, or acoustic waves, in both the air and the solid. (The principle is approximately the same as what causes the vanes to spin in a small whirligig device often used in school science classes, called a light mill or a Crookes radiometer.) Periodic vibrations that propagate within the material create compressional sound waves. But in the solid, an additional kind of sound wave, called a shear wave, involves motion of the atoms in a direction transverse to the direction of propagation, but without any associated temperature change. All are potentially useful for sub­ surface imaging because they can scatter and reflect from internal elastic features, producing “echoes” that return to the surface with information about those features. By Science History Images/Alamy Stock Photo measuring the tiny vibrations The photophone, a less well-known invention on the object’s exterior caused by these of Alexander Graham Bell, used sunlight to effects, one can locate the back wall of carry voice information. Bell observed what is the object or see an otherwise hidden now called the photoacoustic effect, the generdefect inside it, such as corrosion in an ation of sound waves by the rapid expansion airplane, cracks in a weld, defects in and contraction of air over a heated surface. red-hot steel coming out of a mill, or The physical phenomena involved voids in 3D printing, as well as visualize in Bell’s experiment are considerably microstructure evolution in uraniummore complicated than he realized at zirconium nuclear fuel alloys, blood the time. When light is absorbed at the vessels in the eye, or tumors in the body. QUICK TAKE

Opaque objects that are illuminated do not reflect all of the light that hits their surfaces; some of the light is absorbed and can create vibrations within the material.

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Lasers can both create and detect ultrasonic wave signals, which are modified by defects or other structures inside the opaque material and produce a measurable signal.

Peering inside opaque materials without touching or damaging them is useful in manufacturing inspection, infrastructure monitoring, landmine detection, and medical imaging.

Courtesy of Tecnar

A red-hot stainless steel tube passes under a laser ultrasound inspection system directly after leaving a furnace. A pulsed laser generates ultrasound in the pipe, which reflects within its walls and then is measured by a second laser setup. This noncontact system provides immediate feedback for quality control. Laser-based ultrasound can be used to image the interiors of a variety of opaque materials, from aircraft components to human eye tissue.

Optical Detection Because the effects of subsurface elastic features show up as vibrations of the surface, they can be detected optically. Thus, light can indeed be used to see the interior of an otherwise opaque object, without making any physical contact. The process is called laser-based ultrasound. Pulsed laser beams “ping” the object to generate high-frequency sound waves, which are detected by low-power lasers that remotely sense the mechanical vibrations on its surface. One can view this process as being a form of sonar. The subtle vibration patterns detected by these optical methods can reveal features buried beneath the surface of the object. These features include the thickness of the sample, hidden cracks, delaminations, voids, disbonding, and material inhomogeneities. The ability to use echo ranging allows, for example, for in-process monitoring of the dimensions of manufactured parts, which, with real-time www.americanscientist.org

feedback control, can result in a higher yield of products that are within specifications. The noncontact, light-based method can be used, for example, to inspect aircraft for subsurface corrosion, microcracks near rivets, or degradation to the coatings of turbine engine blades. Light-based inspection systems can be applied on size scales ranging from aging infrastructure (bridges, buildings, railways, aircraft, and naval vessels) to semiconductor microchips, wafers, or objects produced by 3D printing (also called additive manufacturing). For many applications, it is crucial that the measurement be entirely optical, either because the objects are otherwise inaccessible, or because there is a need for extreme cleanliness. For example, by using the remote capability of optical probes, one can inspect parts moving along an assembly line without interrupting their progress along the line. Also, because light probes do not require fitting a transducer to the surface, objects with irregular shapes can be in-

spected, such as composite sections of automobiles or jet aircraft components. Moreover, these probes can be configured to inspect parts in vacuums (such as outer space), in radioactive environments, or in other adverse conditions where one cannot easily reach the part or when it is impossible to contact the part during manufacture. For instance, laser ultrasound is used to measure the thickness of rapidly moving red-hot seamless steel tubes as they exit the furnaces of steel mills (see figure above). Light into Sound When pulsed laser light is absorbed by an opaque object, a pulse of sound is generated. To create frequencies in the ultrasonic range (hundreds of thousands to trillions of cycles per second), short laser pulses are required: Pulse times range from tens of microseconds to less than picoseconds. The energy in the optical pulse is in the range of tens of millijoules, which is equivalent to the energy of a U.S. penny dropped from a height of 40 centimeters. Thus, the opaque object is “pinged” by the optical pulse. Laser-based ultrasound can be generated using either of two optically induced mechanisms: the thermoelastic 2023

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effect or ablation. In the create two optical beams ultrasound workpiece generation former case, the opaque that combine (or interfere) material is rapidly heatat the detector. When one ed at laser intensities in beam is shifted in space or the range of hundreds frequency relative to the pulsed laser of kilowatts or more per other beam, it produces defect square centimeter. The an output change at the resulting high-frequency detector. In this case, the laser thermoelastic expansion ultrasonic signal wave ultrasonic launches the ultrasonic gives rise to this minute receiver waves, as was first demchange, which can be one onstrated in 1963 by Richpart in 10 thousandths of ard M. White, an electrical an optical wavelength (or Adapted from Y. Cheng, et al., Sensors 13:16146. engineer at the University equivalently, 10 billionths of California, Berkeley. In a basic laser-based ultrasound system, the short-pulse laser generates of a centimeter). In this case, the material bulk and surface acoustic waves. These ultrasonic waves (red) scatter from The mirrors used in is not modified or dam- internal defects, and also reflect from the back side of the opaque work- laboratory interferometers aged; it returns to its ini- piece, resulting in surface vibrations that can be probed and detected by typically have a surface a laser ultrasonic receiver located on the surface. The signal output (blue roughness that is no more tial state, unaltered. The second mecha- waves) will be affected by the scattering from defects within the material, than a fraction of an optinism, laser ablation, in- providing a means of detecting flaws or other subsurface characteristics. cal wavelength. Howvolves applying intensiever, the surface of the ties of tens of millions of watts or more Signal Received reflecting object, such as an airplane per square centimeter over a small area A second, low-power continuous oper- fuselage or a welded part, can have a of the surface. This results in surface ating laser, or a long-pulse laser, probes surface roughness that is thousands of temperatures of thousands of degrees the surface of the vibrating object and, times greater than that. A probe laser over time periods of 10 billionths of a like what happens in radar, can sense beam that reflects from such an unsecond. The intense heating causes a the Doppler-shifted light as it reflects polished surface will scatter over large small amount of material to be blown from the surface into the detector. The angles into a pattern of laser spots, away from the surface, with the recoil frequency of the probe beam is modu- called speckle, which is deleterious to of the surface generating an intense lated by the surface vibrations, and it sensitive detectors. compressional sound wave. is these minute vibrations that contain Furthermore, low-frequency meThe patterns of the ultrasonic beams the desired ultrasonic information. The chanical vibrations in a hangar or facthat propagate into the object depend speed of the vibrating surface is only tory setting can have amplitudes in the range of a millimeter or so, one million times greater than the ultrasonic surface displacements to be detected. This combination of surface roughness and vibrations would render most interferometers useless as sensors. To overcome surface roughness and vibration difficulties, in the 1980s physicist Jean-Pierre Monchalin of the National Research Council of Canada developed a novel scheme, based on an interferometer invented by French physicists Charles Fabry and Alfred on what excitation mode is used, which about 10 centimeters per second during Pérot at the outset of the 20th century. in turn depends on the geometry of the a typical ultrasonic pulse. Taking this The probe laser light reflected from part and the type of inspection needed. measurement is very challenging: It’s the vibrating sample enters this interIn both cases, sound waves reflect akin to measuring the speed of a crawl- ferometer and bounces back and forth from internal features within the object, ing infant over a time period of only between a pair of partially silvered, whose elastic properties are different 100 millionths of a second. fixed mirrors that face each other. from those of the surrounding material. Such detection sensitivity usually This device acts as an optical resonaUltrasonic echoes from these features requires laboratory conditions, but tor, with sharp peaks in the frequency can be reflected back to the surface this technique has to function in ad- of the transmitted light (analogous to (the mechanism is analogous to sonar). verse environments such as a factory. resonant acoustic modes in a hollow These reflected waves cause surface dis- To achieve this sensitivity, an optical tube). Adjusting the frequency of the placements that are exceedingly small, interferometer is added into the pro- laser to remain on the maximum slope usually in the range of one-tenth of a cess, between the vibrating surface and of one of these resonance peaks makes nanometer to 10 nanometers. By com- the optical detector. A typical optical the device sensitive to the small shifts parison, a single atomic layer is about a interferometer comprises several high- in the frequency of the light reflected third of a nanometer thick. quality mirrors and beam splitters to from the vibrating surface. This detec-

The optical pulse “pings” the opaque object with an energy equivalent to that of a U.S. penny dropped from a height of 40 centimeters.

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percent 80

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Top: From I. Papa, et al., International Journal of Lightweight Materials and Manufacture 4:37. Bottom: From T.-W. Shyr, et al., Composite Structures 62:193.

delamination

matrix cracks due to bending

impact location

surface buckling

fiber breakage

tion technique is similar to tuning in to FM signals on a car radio, which use the resonance peak of an electronic circuit to demodulate that signal. The concept is also similar to that underlying gravitational-wave optical detectors, except in that case, the mirrors move in response to a gravity wave instead of a surface vibration. Another class of laser ultrasound receiver is referred to as an adaptive interferometer, which is sensitive to the minute vibrations of a mirror—in this case, the part undergoing inspection. This interferometer, called a two-wave mixer, was also invented at the National Research Council of Canada by Alain Blouin, Monchalin, and their colleagues, in the 1990s. It uses a photo­ refractive crystal to optically process two input laser beams. One beam is a reference wave, called a local oscillator. The second beam is the light that scatters from the unpolished, vibrating part undergoing testing, called a signal beam. This latter beam contains the ultra­sound information to be detected. Both beams combine (or interfere) to form a real-time, or dynamic, hologram in the crystal. The hologram matches the wavefronts of the reference beam to those of the signal beam to compensate for surface irregularities. It is also referred to as an adaptive photodetector www.americanscientist.org

matrix cracks due to shear

Impact damage can result when a blunt object strikes the exposed surface of a fiber-reinforced polymer composite material. Sometimes the exposed surface shows no signs of damage (above left), but the impact may nevertheless have caused internal delamination, matrix cracking, fiber breakage, or perforation (lower left). Such impact to aircraft, for instance, can result from hail, bird strikes, runway debris, or tools dropped during maintenance. Laser-based ultrasound generation can reveal the hidden subsurface impact damage via ultrasound spurious reflections (above right; color scale indicates the strength of the returned signal). In this case, detection was aided with squirter sensing, in which a water-jet coupler contacts the test part and guides the ultrasound along the stream.

because it tracks the signal beam in time to account for workplace vibrations. The pair of matched beams then hit an optical detector, with its electrical output revealing the ultrasound signal. This technique functions in the same way as laser communication systems, which, by using adaptive optics, can detect low-level signals that have passed through turbulent atmospheres. A third class of optical interferometer is sensitive to the medium itself between the mirrors: air. When sound waves

basic concept of this type of optical interferometer was developed and demonstrated in the late 2010s by physicists Balthasar Fischer at the Vienna University of Technology and Wolfgang Rohringer and his colleagues at XARION Laser Acoustics in Vienna, Austria. Checking for Flaws Once the difficulties with detection sensitivity were resolved, laser ultrasound began to be used in a variety of applications. Using an adaptive interferometer,

Measuring the speed of the vibrating surface is akin to measuring the speed of a crawling infant over a time period of only 100 millionths of a second. travel across the interferometer, they create minute pressure/density waves in the air within the interferometer. The changes in density result in changes to the refractive index of the air, which in turn affects the optical output of the interferometer. One can view this system as a very sensitive microphone. The

laser-based ultrasonic signals, sensed at a distance of about 1 meter, have been used to provide real-time, infactory determinations of the wall thicknesses of rough-cut, unpolished, red-hot hollow steel tubes (with 10micron precision out of 10-millimeter wall thicknesses), moving at speeds 2023

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A0 30

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in excess of 4 meters per second along an assembly line, and at temperatures in excess of 1,000 degrees Celsius. The wall thickness is determined by measuring the time it takes for the ultrasound and its echoes to reflect within the thin walls of the tubes. In a related application, it is important to monitor the strength of a material as it is processed or cast (such as nuclear fuel rods) in a vacuum chamber. Internal granularities and microstructure, which affect the integrity of a material, can be ascertained by measuring the absorption of ultrasound as it reflects between two surfaces of the part and measuring the strength of the 356

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Lamb waves, a type of guided wave in a plate, are generated by laser pulse (at A0), and can be used to inspect carbon fiber reinforced polymer laminates for damage (at S0). An area of damage (top) is encountered by a Lamb wave front, which causes a phase delay (at 40 microseconds) and reflections (at 50 microseconds) that result in the scattering of the incident wave (bottom).

echo signals with a probe beam. Highly attenuated echoes are indicative of ultra­sound waves that have been extensively scattered by relatively large grain sizes or detrimental microstructure. In-situ inspection is also important to detect defects in real time during 3D printing, such as one type called laser sintering, which uses a high-power laser to solidify material on the top of a powder bed in a zig-zag pattern, after which a new layer of powder is deposited. Cliff J. Lissenden of Pennsylvania State University and his colleagues developed a technique using an ultrasound short-pulsed excitation laser, the output beam of which is formed into a line source that generates ultrasonic surface waves that probe the processed region. A low-power, long-pulsed probe laser beam senses the resultant vibrations on the same or opposite side of the printed area. Spurious reflections or transmission “gaps” are signs of a defect. Imaging subsurface impact damage in composite structures is also a critical inspection need. Impact damage is particularly insidious in composites because most often no visible signs appear on the surface. Thus, when a tool is dropped on a composite surface, a mechanic may conclude that no damage occurred, when in fact the impact may have caused extensive subsurface delamination (cracks, fiber breakage, and the like). Laser-based ultrasound has been used by Nobuyuki Toyama and his colleagues at the National Metrology Institute of Japan to detect evidence of impact damage by stimulating ultrasonic waves that are guided along a composite plate, called Lamb waves, to interrogate an area in the region of the suspected damage. The Lamb waves propagate along the plate like small water waves, where they are detected by a laser ultrasonic receiver. The presence of impact damage disturbs the Lamb waves just as a stationary rock would interfere with water waves. Hidden Patterns Another application of laser-based ultra­sound is in microelectronics. Inte-

grated circuits in semiconductor chips have electrical connections that are made via solder bumps about 500 microns in diameter, and the area around them is filled with epoxy. Intelligent Optical Systems and one of us (Murray) have shown that laser-based ultrasound can be used to perform nondestructive, noncontact testing to determine that all solder bumps are properly bonded. In another demonstration by HRL Laboratories, a laser ultrasound system was used to ensure that there were no epoxy underfill voids or gaps. In much the same way, these systems have been used to detect epoxy voids or debonding in nuclear radiation shielding. The silicon wafers used in microelectronics can themselves be inspected with a type of laser-based ultrasound called picosecond metrology, whereby ultrashort laser pulses (lasting about 100 femtoseconds, or one-tenth of a trillionth of a second) give rise to ultrashort sound waves when absorbed by a semiconductor chip. The sound waves reflect from the chip’s thin layers, and a delayed laser probe beam measures these time-dependent changes in reflectivity, thereby revealing the thickness of the chip’s thin films down to angstroms in resolution, as pioneered by Humphrey Maris of Brown University. Recently, Stefan Edwards and his colleagues at the Advanced Research Center for Nanolithography in Amsterdam used this technique to reveal

laser array

test landmine

Courtesy of V. Aranchuk, University of Mississippi

A buried unarmed test landmine (circle) is scanned from a moving vehicle by an array of laser beams (red dots, moving in direction of arrow). An audio source induces vibrations that are altered by the buried object, and the vibration pattern difference is detected by the laser system (inset at top right). The system has the potential to find plastic landmines, which are difficult to detect with other methods, such as ground-penetrating radar. The noncontact method can be performed at a safe distance.

Under the Surface Inspecting below an opaque boundary can at times be dangerous, such as in looking for landmines. The best approach is to use long standoff distances. In a recent demonstration of landmine detection, performed by Vyacheslav Aranchuk and his colleagues at the University of Mississippi, an array of loudspeakers insonified a distant area in a field. Sound waves penetrated the ground and reflected from underground objects—including unarmed test plastic explosives that ground-penetrating

A Tight Connection

amplitude

time of flight

From J.-F. Vandenrijt, et al., Proceedings ICEM18 2(8):455.

Laser ultrasound can be combined with robotic scanning (bottom left) to image composite structures (top left) such as ones found in aircraft parts. Irregularly shaped parts can be inspected by a laser beam because the spot where the excitation light is absorbed by the part generates a compressional wave perpendicular to the surface, independent of the angle of incidence. Test flaws marked on the sample are revealed by changes in the amplitude (top right) and the time of flight (bottom right) of the returned scan signal, shown here in false color.

weld joint, resulting in a decreased signal, or even no signal at all (see figure below). Such a diagnostic was installed directly downstream of a laser welder, with the ultrasound generation and probe beams straddling the weld seam, yielding information in real time, with the ultimate goal of providing immediate feedback to the welder system. A key area of ongoing research is the use of laser ultrasound to perform nondestructive testing of spot welds. The average car contains about 5,000 spot welds. Traditionally,

Welding is ubiquitous across most sectors of manufacturing, from microelectronics to the medical sector, the automotive industry, aerospace, and infrastructure. A preferred goal is to inspect weld joints during manufacturing in a nondestructive manner, although in some cases, it is practical to perform the inspection post-processing or offline. Laser-based ultrasound has the capability to perform both in adverse environments. As an example, a weld joint of an automofused flux fused flux generation generation bile automatic transmission reverse clutch detection detection housing can be inspected offline, as demonstrated by Gilmore J. Dunning, Phillip V. Mitchell, and one of us (Pepper) at HRL Laboratories in Malibu, California, by “pitching and catching” the laser beams on opposite sides of the workpiece. Two laser beams (the normal weld: full penetration lack of penetration ultrasound exciter and probe beams) were wave diffracts from bottom of weld scanned across the weld seam. In the case of a good weld, a high transmission of the ultrasound signal is expected when both beams are on testing is done with intermittent destructive inspection, but weld-center, and the signal is expected to decrease sym- obviously not all welds can be inspected in this manner, metrically on either side of the weld bead. In current so the quality of the welds becomes a matter of statistics. manufacturing, welds are inspected destructively, at ran- In some cases, overwelding is a means of attaining some dom, by sectioning selected workpieces to view the weld form of reliability, but it increases production costs. By bead. The ultimate goal is to implement nondestructive using pulsed lasers to generate ultrasound on one surface in-line inspection. of a metal sheet, the ultrasound wave will travel through In a later demonstration, performed by Marvin B. Klein the spot-weld unabated, and through the second sheet in and Bradley L. Bobbs at Intelligent Optical Systems in the case of a good weld. In the case of a bad weld (either Torrance, California, an in-line laser-based ultrasound a poor-quality weld bead or a small-diameter weld spot), inspection system was designed and demonstrated to spurious acoustic reflections will occur that will be detected inspect a weld seam during the actual welding process. by the probe laser of the receiver. The optical microphone A good quality weld will not interfere with the passage of detection system developed by Wolfgang Rohringer and the ultrasonic wave; a weld defect will result in spurious his colleagues at XARION Laser Acoustics detects laser reflections of the ultrasound signal in the vicinity of the ultrasonic waves to image spot-welds nondestructively.

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Courtesy of Intelligent Optical Systems

hidden patterns beneath opaque thin layers. The hidden structure imprints a pattern onto the sound wave, which diffracts the delayed probe beam. This technique can be useful in the microelectronics industry, in which it is critical to align various buried patterns (such as those that form circuits) with subsequent thin layers of material.

From Z. Hosseinaee, et al., Scientific Reports 12:4562.

Photoacoustic remote sensing is used to image the vasculature of a mouse retina (top left). Smaller vessels are visible (top right) and arteries (red arrows) and veins (blue arrows) can be distinguished (bottom left). The method can measure levels of oxygen saturation (abbreviated SO2) in hemoglobin in retinal blood (bottom right). Poor retinal oxygen saturation is indicative of diseases such as diabetic retinopathy and age-related macular degeneration.

radar cannot easily detect—which created minute surface vibrations. An array of laser beams scanned and probed the surface to detect these vibrations. A challenge here is to collect sufficient laser light from the ground to result in a reasonable signal. Speckle compensation may provide a viable solution. An exciting application of laser-based ultrasound is in the field of medical imaging. This novel technique involves the detection of subsurface features in tissue, such as blood vessels and tumors, and its name heralds back to Alexander Graham Bell’s original discovery. The technique, called photoacoustic imaging, employs pulsed or modulated lasers that harmlessly penetrate centimeters into the skin. The modulated light is preferentially temporally absorbed by hemoglobin in the blood. The laserbeam modulation is sufficiently short in duration (lasting tens of microseconds to nanoseconds) that it doesn’t just gener358

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ate heat pulses but also generates ultrasound in hemoglobin-rich features via the thermoelastic effect. These features thus function as subsurface “sources” of ultrasound, as reported in 2016 by Keerthi S. Valluru and Jürgen K. Willmann who were then at Stanford University. A fraction of the ultrasound disturbance propagates to the surface, where minute vibrations occur, as in conventional laser-based ultrasound. By scanning the ultrasound generation and detection beams across the surface of the tissue, a “photoacoustic image” can be obtained, revealing the presence of subsurface blood vessels or tumors against little background. Lihong Wang and his colleagues at the California Institute of Technology have also performed pioneering work in this area. All-optical imaging approaches such as these may be most suitable for ophthalmology procedures, wound assessment, brain surgery, and laser surgery.

For example, in a recent demonstration by Zohreh Hosseinaee and her colleagues at the University of Waterloo, pressure waves modified the reflectivity of a probe beam to realize in-vivo functional and structural retinal imaging using remote photoacoustic microscopy, revealing not only the vasculature of the retina but also its oxygen saturation. Recently, investigators have explored techniques to further enhance the photoacoustic response of blood. In one case, in vitro experiments were performed by one of us (Murray) and our colleagues using samples of bovine blood, into which were injected 5-micrometer microbubbles, comprising thin spherical membranes housing a molecular species that absorbs light at a much greater rate than blood. Hence, more intense photoacoustic signals would emanate from much smaller volumes than from blood cells within vessels or tumors. The goal is to prepare the surface of these microbubbles with a compound that attaches to, for example, cancerous cells within a blood vessel or tumor, enabling photo­ acoustic mapping of the cancerous species with high precision. In another advance, researchers at MIT Lincoln Laboratory and their collaborators at the Massachusetts General Hospital Center for Ultrasound Research and Translation have developed a new medical imaging device: the Noncontact Laser Ultrasound (NCLUS) system. Developed by Robert Haupt and his colleagues, the goal of the technology is to replace conventional, direct-contact ultrasound imaging of patients with the use of noncontact lasers to generate and receive the ultrasound. This advance would enable the imaging of interior body features such as organs, fat, muscle, tendons, and blood vessels—all without touching the patient. The system can also measure bone strength and may have the potential to track disease stages over time. The laser-based system has the potential to diagnose patients who have painful or sensitive body areas, are in fragile states, or are at risk of infection, as well as to image burn or trauma victims, patients with open deep-tissue regions during surgery, premature infants requiring intensive medical care, patients with neck and spine injuries, and contagious individuals, all of whom require long standoff distances. The system uses a pulsed nearinfrared laser—operating safely in the thermoelastic (photoacoustic) mode—to

generate ultrasound waves at a specific location on the patient, not unlike those of a handheld ultrasound transducer, but without contact. A laser Doppler vibrometer, also operating in the nearinfrared spectrum and at safe power levels, is used to remotely sense the resultant surface ultrasound vibrations. Both lasers are housed in a robotically articulated arm to precisely locate the pair of laser beams on the surface of the patient. A 2D lidar is used to map the surface topography of the patient’s skin; a high–frame-rate, short-wave–infrared camera records the laser source and the projected locations on the skin for the

into a preferential direction of propagation, are being tested. These techniques use multiple light beams that are either properly delayed in time, or strategically distributed along the surface of the specimen, to produce constructive reinforcement (or in other words, focusing) at the desired depth and direction within the sample. This technique is akin to throwing a cluster of small pebbles into a still pond: By carefully tossing the pebbles at specific locations and in a predetermined time sequence, a desired water wave can be generated that can be focused and directed into a given region of the pond. The technique also has been

The laser-based system has the potential to diagnose patients who have painful or sensitive body areas, are in fragile states, or are at risk of infection, all of whom require long standoff distances. receiver, providing the array parameters necessary for constructing ultrasound images. This noncontact ultrasonic system is in the development stage and promises to be a key diagnostic tool in the medical arena. Maximum Resolution How small a feature could one “see,” or resolve, using laser-based ultrasound? The answer depends on how short a laser “ping” is, a geometrical factor, and the wavelength. As an example, consider aluminum, in which the speed of sound is approximately 6,420 meters per second. For a typical laser pulse of 10 nanoseconds (or 10 billionths of a second), the smallest feature that can be resolved is about 78 microns (a human hair is about 50 microns in diameter). Using an ultrashort pulsed laser with picosecond lengths (trillionths of a second), the smallest feature that can be resolved is about 78 angstroms (an atom is about 3 angstroms in length). Processing techniques that remove speckle can improve this limitation significantly, by factors of five or greater. To improve laser ultrasound further, on the generation side, more efficient ways of channeling acoustic energy into a preferential band of frequencies, or www.americanscientist.org

applied in reverse, on the receiving side, by one of us (Murray): Multiple laser ultrasound receiving beams, strategically located on the workpiece, can emulate a synthetic array to detect and analyze the sample with higher resolution sensing of buried flaws and defects at a given location in the workpiece (akin to an imaging microscope). Seeing the Future The use of light and sound to see the interiors of metals, semiconductors, composites, ceramics, and other opaque objects, including human tissue, is no longer just a scientific curiosity but is critical to ensuring the integrity and quality of many manufactured parts and improving medical diagnostics. In the latter case, because light is nonionizing, patients can avoid exposure to potentially harmful x-rays. In the case of airplane components, the safety of passengers can be at stake. Moreover, the safety, lifetime, and performance of satellites, automobiles, nuclear power plants, and the like, which are dependent on the quality and integrity of welds and bonds, can be significantly enhanced through the use of these rapid and contactless inspection techniques. Next-generation factories will need to

be equipped with noninvasive sensors to inspect and certify parts remotely without removing them from an assembly line. But as these techniques show, as long as one can see the outside of an opaque object, one can also view and inspect its interior using light and sound. Bibliography Blouin, A., and J.-P. Monchalin. 1994. Detection of ultrasonic motion of a scattering surface by two‐wave mixing in a photorefractive GaAs crystal. Applied Physics Letters 65:932–934. Blouin, A., et al. 1998. Optical detection of ultrasound using two-wave mixing in semiconductor photorefractive crystals and comparison with the Fabry-Perot. In Nondestructive Characterization of Materials VIII, ed. R. E. Green, pp. 13–19. Boston, MA: Springer. Dewhurst, R. J., D. A. Hutchins, S. B. Palmer, and C. B. Scruby. 1982. Quantitative measurements of laser‐generated acoustic waveforms. Journal of Applied Physics 53:4064–4071. Hutchins, D. A. 1998. Ultrasonic generation by pulsed lasers. In Physical Acoustics, volume 28, eds. W. P. Mason and R. N. Thurston, pp. 21–123. New York, NY: Academic Press. Ing, R. K., and J.-P. Monchalin. 1991. Broadband optical detection of ultrasound by two-wave mixing in a photorefractive crystal. Applied Physics Letters 59:3233. Monchalin, J.-P., and R. He’on. 1986. Laser generation and optical detection with a confocal Fabry-Perot interferometer. Materials Evaluation 44:1231–1237. Monchalin, J.-P. 1991. Optical generation and detection of ultrasound. In Physical Acoustics, eds. O. Leroy and M. A. Breazeale, pp. 65–76. Boston, MA: Springer. Monchalin, J.-P. 2020. Laser-ultrasonics: Principles and industrial applications. e-Journal of Nondestructive Testing 25:1–43. Murray, T. W., and J. W. Wagner. 1999. Laser generation of acoustic waves in the ablative regime. Journal of Applied Physics 85:2031–2040. Noroy, M.-H., D. Royer, and M. Fink. 1993. Transient elastic wave generation by an array of thermoelastic sources. Applied Physics Letters 63:3276–3278. Scruby, C. B., and L. E. Drain. 1990. Laser Ultrasonics. Bristol, UK: Adam Hilger. Wagner, J. W., and J. B. Spicer. 1987. Theoretical noise-limited sensitivity of classical interferometry. Journal of the Optical Society of America B 4:1316–1326. David M. Pepper earned a PhD in applied physics from the California Institute of Technology, and earned a BS in Physics from the University of California Los Angeles, Summa Cum Laude. He was senior research scientist at HRL Laboratories in Malibu, California, for 31 years and is currently owner of Malibu Scientific. He is an inventor on 68 U.S. patents. Todd W. Murray is a professor of mechanical engineering and director of the Laser Acoustics Laboratory at the University of Colorado Boulder. He received a PhD in materials science and engineering from Johns Hopkins University in Baltimore. Email for Pepper: [email protected] 2023

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Memories Within Myth The stories of oral societies, passed from generation to generation, are also scientific records. Patrick Nunn

I

n the 1880s, the American journalist William Gladstone Steel made several visits to a freshwater lake that filled the caldera of an extinct volcano in Oregon. For Steel, these visits were the fulfilment of a dream that began while he was just a schoolboy in Kansas. It was one day in 1870, while reading the newspaper wrapped around his school lunch, that he noticed an article about the “discovery” of a spectacular body of freshwater

named Crater Lake. “In all of my life,” Steel would later recall, “I never read an article that took the intense hold on me that that one did.” When he finally made it to the lake in 1885, he was so captivated that he determined to have the area designated as a national park. But designation was not easily gained and required extensive documentation of the region. To help with the reconnaissance, Steel engaged guides from the local

Klamath peoples, who had occupied the area for countless generations. During their work together, Steel noted that the guides never once looked at the lake itself, instead “making all sorts of mysterious signs and staring directly at the ground”—a sign that the Klamath regarded Crater Lake as a powerful place where a great cataclysm once happened and might happen again. According to Klamath stories, buried deep beneath the lake

QUICK TAKE The abilities of preliterate societies to store, organize, and share useful information across generations are often not appreciated by modern literate societies.

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Multiple examples from around the world demonstrate that oral histories can be thousands of years old, passed down through hundreds of generations.

The survival of our ancestors’ stories is a testament to humans’ capacity to endure through profound, even catastrophic, change, no less important today than millennia ago.

Michael Whyte; USGS

The eruption and collapse 7,700 years ago of the volcano that formed Crater Lake in Oregon is included in the Klamath peoples’ oral traditions. Such oral histories demonstrate the longevity of stories passed down through hundreds of generations. The inset shows the geologic formations above and below the lake’s surface today, including Wizard Island (foreground, in white) and the Merriam Cone behind it (green).

waters is the spirit of Llao, a demon who lived within the volcano that once towered above Crater Lake. In a past age, Llao terrorized the Klamath by showering them with hot rocks and shaking the ground on which they lived. These attacks continued until www.americanscientist.org

Llao was confronted by the benevolent spirit Skell, who pulled the volcano down on the demon and created Crater Lake above. What sounded to Steel like myth is more than just a story. It is a memory of an eruption that caused a volcano

to collapse and form a giant caldera that, as many do, filled with freshwater. The eruption occurred  7,700 years  ago, but the Klamath had preserved its story and even sustained associated traditions, such as not looking directly at the lake. Although 2023

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Wikimedia Commons

20,000

Time since last remembered activity (years ago) 10,000

Lake Pupuke (New Zealand)

Maar stories

Mt. Gambier (Australia) Lago Albano (Italy) Mt. Schank (Australia)

Laguna de Aljojuca (Mexico) Lake Eacham (Australia)

Nunn, et al. 2019.

Lake Euramoo (Australia) ?? Lake Barrine (Australia) ?? 20,000

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Estimated minimum age ranges of formation stories of maars (a type of volcanic crater) around the world highlight their remarkable longevity. Some of the best-documented of these stories are from Lago Albano maar in Italy, shown in the above painting from 1800 by Jacob Philipp Hackert. Stories of the Albano maar, which formed at least 8,000 years ago, were first transcribed about 2,000 years ago.

they did not read nor write when Steel worked with them in the late 19th century, the Klamath people knew a story about an event that had occurred more than  seven millennia  earlier, a story carried across perhaps 300 generations by word of mouth. Many literate people today believe this kind of thing is impossible or, at best, an anomaly, because they evaluate the abilities of oral (or “preliterate”) societies by the yardsticks of literate ones, where information seems far more readily accessible to anyone 0 who seeks it. In doing so, they undervalue the ability of these oral societies

to store, organize, and communicate equivalent amounts of information. In my 2018 book The Edge of Memory, I called this misperception “the tyranny of literacy”: the idea that literacy encourages its exponents to subordinate the understandings of others who appear less “fortunate.” But accounts like Steel’s are beginning to help break apart this idea: Oral traditions, rather than being subordinate, are capable of transmitting just as much useful information as the technologies of reading and writing. The Longevity of Oral Histories In the early 20th century, the French ethnographer Arnold van Gennep spent considerable time familiarizing himself with Indigenous Australian (Aboriginal) oral stories, concluding that these include “fragments of a catechism, a liturgical manual, a history of civilisation, a geography textbook, and to a lesser extent a manual of cosmography.” While later research has documented the nature of this information more fully than Gennep realized, especially in the fields of star knowledge and land management, the focus has shifted recently to those types of Aboriginal knowledge for which an extraordinary longevity can be unequivocally demonstrated. Some of the most compelling examples are of volcanic eruptions that can now be dated with high precision, such as the one that formed Crater Lake in Oregon. These eruptions then become proxies for the age of associated oral traditions. Take the example of the eruption that caused the formation of Australia’s maar crater in which Lake Eacham (in northern Queensland) now lies, an event that local Dyirbal-speaking residents described as follows: The camping-place began to change, the earth under the camp roaring like thunder. The wind started to blow down, as if a cyclone were coming. The campingplace began to twist and crack. While this was happening there was in the sky a red cloud, of a hue never seen before. The people www.americanscientist.org

people have stories about this event, about how the river courses filled with fire— memories of lava flows—and how people were engulfed by “dust” and asphyxiated, details of a kind that retrodictive science is powerless to deduce. More widespread in Australia are Aboriginal stories of coastal submergence, now known from more than 30 locations all around the continent, that are plausibly interpreted as memories from more than  seven millennia  ago when the ocean surface was much lower than today, when shorelines were kilometers—sometimes tens of kilometers—further seaward than today, and when today’s islands were contiguous with the mainland. www.abebooks.com People arrived in Australia around  70,000 years  ago, long before The Lardil storyteller and artist Dick Roughsey (Goobalathaldin) recounted how his the coldest time of the last great ice ancestors arrived on his home islands, now age when the ocean surface was more called the North Wellesleys in Australia, via than  120 meters  lower than it is now, a peninsula from the mainland. The author’s a result of the storage of ocean water work estimates these islands formed from within thick ice sheets that once blanthis peninsula more than 7,000 years ago. keted many continents. When the ice age ended, ice started melting, causing tried to run from side to side but the sea level to rise. This rise continued were swallowed by a crack which for  10,000 years  or more and caused opened in the ground. [Translamassive and ongoing disruption to tion by Robert Dixon of Central people living in these places. We now Queensland University.] know of “submergence stories” from northwest Europe and elsewhere, inMy team’s best estimate for the for- cluding Scottish “myths” about postmation of this volcano—and therefore glacial coastal change—but it is the the narrative describing this event—is Australian Aboriginal stories that gena little more than  9,000 years  ago, as erally contain the greatest detail. we explain in our 2019 paper in the Consider the  account of the Lardil Annals of the American Association of storyteller and artist Dick Roughsey

Ancient myths represent knowledge from times far earlier than those in the world’s oldest books. Geographers. A few hours’ drive southwest from Lake Eacham brings you to the volcano of Kinrara,  estimated by geographer Benjamin J. Cohen of the University of Glasgow and his team to have last erupted around 7,000 years  ago. The local Gugu Badhun

(whose tribal name was Goobalathaldin), who explained how “in the beginning, our home islands, now called the North Wellesleys [Gulf of Carpentaria], were not islands at all; but were part of a peninsula running out from the mainland. . . . The Balumbanda 2023

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former land extent modern land coastline circa 7,500 years ago (sea level was 18.3 meters lower)

St. Martin’s

Tresco Samson St. Mary’s 49°55'N St. Agnes

6°20'W

2 kilometers

Steve Taylor ARPS/Alamy Stock Photo; map courtesy of Patrick Nunn

The Scilly Isles off the coast of England were inhabited 8,000 years ago when the land was one single island (inset). Those people must have told stories about the rapid rise in sea levels that they witnessed, which may have been preserved in Arthurian legends about the lost land of Lyonesse. Today, archaeologists continue to study village ruins and field boundaries there, some submerged or in the intertidal zone, such as this one at Samson Flats.

[Lardil ancestors] people came along that peninsula long before it was cut up into islands.” Geographer Nicholas J. Reid of the University of New England and I estimated that this event occurred more than 7,000 years ago. A remarkable parallel from the other side of the world comes from the Monach Islands in the Outer Hebrides of Scotland. Here, oral traditions collected in the 1860s included stories about times when these islands were connected to the neighboring island of North Uist: Owing to the gradual dislodgment of the friable sand forming the isthmus, the isthmus by degrees gave way to fords, and the fords broadened into a strait. . . . Tradition still mentions the names of those who crossed these fords last, and the names of persons drowned in crossing. 364

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The best estimate for the existence of an isthmus connecting the Monach Islands to North Uist is also around 7,000 years ago. So we have solid evidence from two contrasting geographical and cultural contexts of memories recalling land-bridge submergence events  seven millennia  ago—memories that were, until recently, remembered solely through oral traditions. Though referring to events from millennia ago, these memories were not difficult to recall: In the 1970s and 1980s, Roughsey (Goobalathaldin) filled books with his people’s oral traditions; Mary Mackay, the chief informant for the Hebridean stories, was clearly also loquacious, rendering her “vivid” tales in “felicitous Gaelic” according to Alexander Carmichael, the folklorist who collected them during the 1860s.

The Importance of Collective Memory These tales of rising oceans are not mere stories. Despite occasional embellishment, their empirical skeletons are easy to recognize. Is it likely that our ancestors across the world sat around inventing stories about times when two landmasses were joined, and insisted on communicating these improbable fictions downstream along the river of history? Or is it more probable that these stories were passed along because people remembered an event so foundational to local history that it was considered hugely important to communicate to each new generation? Of course, in contexts where there has been considerable mixing of cultures, some of these stories have become mythologized—populated by supernatural beings capable of feats no human could match. Take the example of the giants who feature in myths and legends in every part of the world. Imagine you are trying to tell your ancestral story about how Ireland was once connected to Scotland and Wales, or how Tasmania was formerly contiguous with mainland Australia.

Your audience looks skeptitance to believing such stocal, so you rationalize your ries survived through miltale, stating that in the old lennia of oral tradition? The days people were giants, “tyranny of literacy” makes which is how they were able us skeptical of knowledge to stride across the expanses being retained in oral societof water that people could ies for such a long time. Yet, see. Your audience is satisas awareness of the empirified and interest in your stocal foundations of “myths” ry has been recharged, enand “legends” grows, such suring that it will be retold. skepticism seems fated to But your story has also been disappear. transformed, from narrative Many of us assume that to myth, meaning it could people in oral societies were be regarded as a fanciful or unable to access and utilize puerile invention dismissed the amounts of information millennia later by literate that we do. But few literate people as having no value peoples have considered the beyond entertainment. implications of this assumpThese “myths” are not tion: If people who do not fiction. Most of the ancient read or write cannot store myths of long-established or utilize the knowledge cultures have an empirical of their ancestors, then we core. They are not inventions must conclude that we are but observations, filtered here today by luck—luck through worldviews from that would have needed to potentially thousands of last around 250,000 years, as years ago and clothed with long as modern humans Courtesy Patrick Nunn layers of narrative embel- When they met in 2004, Maikeli Rasese told the author the history have stridden across Earth. lishment before they reach of Yadua Island in Fiji, including the people who had lived along its You may think my views us today. Framed within the coast over the past few generations and a past tidal wave and ship- here are extreme. Stories science of their day, they wreck. He demonstrated to the author the sheer breadth of memory carried across centuries and represent knowledge often necessary to keep these oral histories alive. millennia are one thing, but from times far earlier than can these memories really those in the world’s oldest books. to 5,000 years ago when the rapid rise pass to us from much deeper in time? Victorian-era archaeologist  O. G. S. of the ocean turned a single large isCrawford, an irascible, unconventional, land into a series of smaller islands (see My Oral History Education yet hugely influential figure, pondered map on page 364), much to the alarm, Many of the longest-­enduring human the veracity of these “myths” with we can infer, of its inhabitants. The cultures have ancestral knowledge characteristic forthrightness. His focus land is unlikely to have been called that in some cases is several hundred was on the stories of the “lost land” of Lyonesse off the southwest tip of England. In the inaugural issue of the journal  Antiquity  (which he founded in 1927), Crawford asked whether “the famous legend of Lyonesse . . . had . . . any real basis in fact, or is it merely an invention of the ‘dreamy Celt’?” Crawford found “good reasons for believing that the substance of the legend is true,” but it is hard to find many people since who have agreed with him. Lyonesse—­that name seems to have years old and has undoubtedly been Most commentators conclude Lyonesse been introduced during the Arthu- key to their survival. Countless anto be an “imaginary territory,” a place rian era around the  sixth century— thropologists and archaeologists have to accommodate historical romance but there is robust evidence that the shown that human societies can retain and the birth of nationalist identity— Scillies were inhabited 8,000 years ago knowledge for centuries, pointing to ultimately, it’s seen as a lure for tour- when the archipelago was largely a the reciting of genealogies as a comists. Few scientists dare admit it to the single island. There is also evidence mon example. But survival requires realm of rationalist thought. that people witnessed the gradual more than lists. It requires people to Yet the core of the Lyonesse stories fragmentation of that island during understand their deep geographical is almost certainly true. They plau- the following millennia. It is easy to and historical context, their place in sibly represent the observations of believe those people told stories about the world and how to sustain it. I sugpeople living on the Scilly Isles 4,000 what happened, so why is there resis- gest that our distant ancestors and

Many literate people undervalue the ability of oral societies to store, organize, and communicate information.

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Wikimedia Commons/Charbel Zakhour

Oral traditions can only be preserved if people are able to learn them. These stories require comfortable, relaxed environments, such as sitting around a fire at night. Anthropologist Polly Wiessner of the University of Utah has emphasized that group interactions around a fire are foundational to the creation and communication of oral traditions.

their societies were no less risk-aware or risk-averse than we are today. Their underlying goal was for their bloodline to endure, which is essentially why today we educate young people, teaching them reason, giving them an understanding of the world they inhabit so they might survive. Reason does not depend on books but on acquiring and processing knowledge from whatever sources are available

educated literate people—that orality is inferior to literacy. As carefully explained by Walter Ong in his classic 1982 book Orality and Literacy: The Technologizing of the Word, not only has literacy transformed human consciousness, shifting it from soundfocused to sight-focused, but it has also “weaken[ed] the mind.” As Ong wrote: “Those who use writing will become forgetful, relying on an external

I realized I had been privileged to witness the expounding of oral traditions at their best. and are best aligned with what we need to know in order to survive. My earliest encounters with people who could neither read nor write (nor, in this case, speak English) were in the Pacific Islands, where I lived and worked for more than two decades. As a geologist, I conducted research in some of the remotest corners of the Pacific region, where my self-belief as a conventional scientist gradually eroded and was replaced with an appreciation of other worldviews equally as valid as that with which I had been inculcated. I also became disabused of the belief—held by most Western366

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resource for what they lack in internal resources.” Plato’s Socrates noted the same thing, arguing that writing “destroys memory,” something that sustained oral societies in every part of the inhabited world for tens of thousands of years. If there was a pivotal moment in my journey toward an awareness of the depth and breadth of oral knowledges, it was late one afternoon in 2004 when, with some colleagues from the Fiji Museum, I started a conversation with a man named Maikeli Rasese at his home in Denimanu Village, the only settlement on Yadua Island in north-

ern Fiji. We wanted to learn something about the human history of Yadua, of which Rasese was the foremost authority. He described to us each coastal embayment in turn, relating the stories of the people who had occupied it over the past few generations, along with eventful moments in its history, such as a shipwreck, a tidal wave, even the heroic repulsing of invading forces. None of these details were written down. All of it was in his head. And all of it came from his lips in perfect order, fluently, as though he had been reading from a text in front of him. After a few hours, as we neared the end of our narrative circumnavigation of Yadua—not, by any measure, a large island—I assumed we would shortly conclude our evening. But Rasese was not finished. Having exhausted his historical knowledge of the island, he proceeded to explain where its people had come from originally, how they had abandoned their previous homes on other islands because of growing aggression from new arrivals, and how others of their clan had dispersed but remained in touch, periodically renewing their ties, sometimes through intermarriage, sometimes through the ritualized exchange of traditional valuables. It was  2 a.m.  when, seeing his audience drooping with fatigue, Rasese finally ended his storytelling. The next day, while contemplating the voluminous notes I had made that evening, I realized that I had been privileged to witness the expounding of oral traditions at their best. Such exposition is how it had once been for every group of humans on Earth. Telling these stories was how we optimized our chances of survival, a successful strategy for making sure every new generation was aware of what the previous generation had known. Under optimal conditions, oral societies were able to pass on knowledge in a coherent form across hundreds of generations to reach us today. We know that oral memories of volcanic eruptions go back more than  7,000 years  in several instances; numerous stories of coastal submergence (attributable to postglacial ocean rise) are likely to be of a similar age, some perhaps more than  10,000 years old. The edge of memory is indeed a time horizon of extraordinary antiquity, one that gives us renewed respect for our preliterate ancestors in every part of the world.

Half a century ago, people might remember 10 or 20 telephone numbers, but today how many? Smartphones have almost removed any need to remember phone numbers, birthdays, addresses, or even names. These developments can make life easier, no question, but they also encourage us to undervalue what we have lost. Humans have a deep-rooted affection for narrative that, I suggest, was born long ago in oral societies. In those times, listening to the stories of your elders was mandatory, not optional. If you didn’t listen, you couldn’t learn. And if you didn’t learn, you wouldn’t likely survive. So strong was the communal will to survive that everyone learned—there was no choice. People in oral societies learned to be attentive listeners and, later in life, habitual storytellers. But good storytellers don’t just tell stories. They do whatever they can to engage  their listeners, something that applied as much thousands of years ago as it does today. Storytellers perform, they sing and dance, they mimic and entertain. And therein lies the deep roots of what has been ringfenced in today’s literate societies as theater, poetry, dance, and even art. It seems clear that ancient rock art, for instance, had little to do with beauty (although today we often laud its aesthetic qualities) but everything to do with practical wisdom. Such art, it seems, provided memory aids for knowledge-holders, perhaps to populate particularly difficult-to-remember details of important stories. Literate people inherited these things from their preliterate ancestors but repurposed them as cultural creations, not knowing what else to do with them. In Community with Ancestors Where does that leave us, today? In contemplating the extraordinary longevity of oral traditions, I think it is key to consider the importance of context. It seems obvious to suppose that people learn better when they are relaxed, in an environment where they feel comfortable, where they and their peers are eager to learn. One of the scholarly works that influenced my thinking on this subject was anthropologist Polly Wiessner’s insightful research at the University of Utah about the cultural impact of gathering around a fire at night. She suggests that firelight extended group interactions into the night, creating new www.americanscientist.org

opportunities for “singing, dancing, religious ceremonies, and enthralling stories” that laid the foundations for the creation and communication of oral traditions. Most of us have felt this phenomenon: There is something primeval about staring into the night-shaded face of a tamed fire, aglow and crackling. It opens a conduit to the past. Perhaps the greatest lesson we can learn from the nature of ancient stories is that we have been here before, confronting an enduring and profound challenge from climate change that is likely to force major changes to the ways most of us live. But we can take some comfort from the fact that our ancestors survived something comparable:  10,000 years  of rising temperatures and sea levels that followed the end of the last great ice age, forcing changes in coastal geographies to which people had no option but to adapt. Our ancestors survived, as did some of their stories, which record their experiences of adaptation as familiar places were submerged and as landmasses broke into islands. We too shall survive, nurturing stories that will one day, thousands of years from now, help  our  descendants survive. That is the way of this world. Bibliography Barber, E. W., and P. T. Barber. 2005. When They Severed Earth from Sky: How the Human Mind Shapes Myth. Princeton, NJ: Princeton University Press.

Kelly, L. 2017. The Memory Code: Unlocking the Secrets of the Lives of Ancients and the Power of the Human Mind. London: Atlantic Books. Nunn, P. D. 2018. The Edge of Memory: Ancient Knowledge, Oral Tradition and the Post-Glacial World. Sydney: Bloomsbury. Nunn, P. D. 2020. In anticipation of extirpation: How ancient peoples rationalized and responded to postglacial sea level rise. Environmental Humanities 12:113–131. Nunn, P. D. 2021. O cei na vulavula? Insights and regrets of a foreign geoscientist in the Pacific Islands. Geosciences 11:182. Nunn, P. D. 2021. Worlds in Shadow: Submerged Lands in Science, Memory and Myth. Sydney: Bloomsbury. Nunn, P. D., et al. 2022. Human observations of late Quaternary coastal change: Examples from Australia, Europe, and the Pacific Islands. Quaternary International 638– 639:212–224. Ong, W. J. 1982. Orality and Literacy: The Technologizing of the World. New York: Routledge. Roughsey, D. (Goobalathaldin). 1971. Moon and Rainbow: The Autobiography of an Aboriginal. Sydney: Reed. Whiteley, P. M. 2002. Archaeology and oral tradition: The scientific importance of dialogue. American Antiquity 67:405–415.

Patrick Nunn is professor of geography at the University of the Sunshine Coast in Australia. His latest books are  The Edge of Memory: Ancient Stories, Oral Tradition and the PostGlacial World  (2018) and  Worlds in Shadow: Submerged Lands in Science, Memory and Myth  (2021). He lives in Bokarina, Queensland. This article is adapted from one that appeared in Aeon, aeon.co. Email: [email protected]

Announcing a call for entries for the

George Bugliarello Prize

The George Bugliarello Prize is awarded to a superior interdisciplinary essay, review of research, or analytical article published in American Scientist magazine. See for more information at sigmaxi.org/programs/prizes-awards/bugliarello-prize

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Beautiful Armor The rich variety of mollusk shells reflects the diversity of the phylum, which has fascinated humans for millennia. Andreia Salvador

Fascinating Shells The beautiful shells pictured here belong to one of the most diverse groups of animals on the planet: mollusks. These invertebrates include snails, oysters, cuttlefish, and chitons, each with their own characteristic type of shell. Most snails have a spirally coiled shell, oysters have a pair of shells called valves, cuttlefish have an internal shell, and chitons have an armorlike shell made up of eight separate pieces. And some mollusks, such as slugs, do not have a shell at all. For those mollusks that have one, their external shell provides protection for the soft body. The shell is made of calcium carbonate and a tough protein called conchiolin, which forms the shell matrix into which the calcium carbonate is deposited. Both components are secreted by the mantle, a thin layer of tissue that covers the soft parts of the mollusk’s body. As the animal grows, more shell is secreted by the mantle, enlarging the shell. All of the shells featured here come from collections held by the Natural History Museum, London. The size given for each shell refers to its largest dimension (including any spines or other ornaments). The accompanying geographic distribution information gives the known range of the species. Andreia Salvador is a senior curator of marine mollusca at the Natural History Museum, London. Photos and text are excerpted and adapted from Fascinating Shells: An Introduction to 121 of the World’s Most Wonderful Mollusks by Andreia Salvador, published by Natural History Museum, London, and the University of Chicago Press. ©  2022 by The Trustees of the Natural History Museum, London. Email: [email protected] 368

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Money cowry Monetaria moneta Distribution Indo-Pacific Size 15 millimeters

Money Cowry In many parts of the world, until the end of the Roman Empire circa 500 CE, this little shell was used as currency. It continued to be used as small change in the markets of Benin, Ghana, Ivory Coast, and Burkina Faso into the 20th century. Many factors contributed to the shells’ success as money, but probably the most significant were that they could not easily be counterfeited (though imitations were produced from bones, ivory, stones, and bronze), they were a convenient and constant size, and they were durable and could be transported easily, like coins. In 18th-century Uganda, one could purchase a cow for 2,500 of these shells, a goat for 500, and a chicken for 25.

Paˉua Haliotis iris Distribution New Zealand Size 125 millimeters

Pa¯ua The shell of a mollusk is made almost entirely of calcium carbonate, which the animal extracts from food and seawater. The three layers of the shell are formed simultaneously by the mantle. The outer layer, or periostracum, is usually brown or black in color, or is absent in some groups. The second layer, or ostracum, is formed of calcite crystals, and the third layer, or hypostracum, is formed from aragonite (both calcite and aragonite being different forms of calcium carbonate).

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In some mollusks, the aragonite crystals cement together in overlapping layers to form mother-of-pearl, or nacre. The iridescent colors of nacre are not produced by pigments in the shell but instead are derived from the physical properties of the crystals. Shells that have nacre are polished and carved to make jewelry, buttons, or decorative objects. The paˉua, a species of abalone that is only found in New Zealand, is renowned for its blue and green iridescent mother-of-pearl.

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Purple Dye Murex For thousands of years, people have known how to extract dye from mollusks. The Phoenicians of Tyre in southern Lebanon perfected the process for making a dark reddish-purple dye known as Tyrian purple. This long-lasting dye was taken from several species of whelks, including the purple dye murex, Bolinus brandaris, and the banded dye murex, Hexaplex trunculus, which are found on the Mediterranean and Atlantic coasts. When a murex is disturbed, it retreats into its shell and ejects a fluid, which initially is colorless but, once exposed to sunlight, gradually turns from yellow to green to blue and finally to a purplish red. The dye was ­expensive—for one gram of dye, more than 10,000 snails were needed. For this reason, the dye was reserved for the garments of individuals of the highest rank. Today, synthetic versions of such pigments are manufactured. Purple dye murex Bolinus brandaris Distribution Portugal, Spain, Morocco, Mediterranean Sea Size 70 millimeters

Windowpane oyster Placuna placenta Distribution Tropical Indo-West Pacific Size 150 millimeters

Annam Amphidromus The direction in which a mollusk shell’s whorls are coiled is an important characteristic. The majority of shells are coiled clockwise (dextral), but a few species coil counterclockwise (sinistral). However, amphidromus tree snails are unusual; they are chirally dimorphic, meaning that in the same population one can find both dextral and sinistral individuals. One reason for this variation could be related to their natural predators, snakes. Most snail-eating snakes of the genus Pareas have elongated teeth on the right mandible, and for that reason specialize in predation on the dextral shells. These snails have evolved by coiling the other way, which makes it difficult for the snake to grasp and eat them.

Annam amphidromus Amphidromus inversus Distribution Southeast Asia Size 45 millimeters

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Windowpane Oyster The windowpane oyster is one of the most flattened bivalve mollusks. Its greatly compressed valves hardly leave room for the animal, which lies on the right valve. This oyster is abundant on the muddy bottoms of quiet lagoons, bays, and mangroves in the tropical Indo-West Pacific. It feeds mostly on plankton and organic detritus. Its shell is thin, brittle, and translucent, with a pearlescent appearance, and its outline is nearly circular. This species’ common name is derived from its long-standing use in windowpanes in place of glass in various Asian countries. The shells can still be found in the windows of old homes in the Philippines, where they are fished in large numbers and are also manufactured into screens, lampshades, and ornaments.

Horned helmet Cassis cornuta Distribution Red Sea, Indo-Pacific Size 270 millimeters

Horned Helmet Coral reefs are one of the richest and most diverse environments on Earth, providing complex and varied marine habitats that support a wide range of organisms. They cover less than 1 percent of the global marine ecosystem, yet they provide a home for 25 percent of all marine species, including thousands of mollusk species. But coral reefs are under threat worldwide. In addition to anthropogenic challenges, one major concern is the crown-of-thorns starfish. These starfish can grow as large as 1 meter in diameter, and they feed on coral. The horned helmet is one of the few species of mollusk that predate on the crownof-thorns starfish. For this reason, the horned helmet has been put under strict protection in Queensland, Australia, in a bid to prevent the starfish spreading and consuming the Great Barrier Reef. www.americanscientist.org

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Zigzag nerite Vittina waigiensis Distribution Southwest Pacific Size 15 millimeters

Zigzag Nerite West Indian worm shell Vermicularia spirata Distribution Northwestern Atlantic Ocean, Caribbean Sea, Gulf of Mexico Size 100 millimeters

These colorful freshwater snail shells are a wonderful example of the diversity in molluscan shell color, and, although the pattern on each is different, they are all representatives of the same species. Such variable appearance within a species is known as polymorphism. The advantage of looking different is possibly very easy to explain: If they all looked the same, predators would only have one pattern to recognize when hunting. With many different patterns, the zigzag nerite confuses predators by making it difficult to establish a consistent search image of their prey.

West Indian Worm Shell Most gastropods have regular, neatly coiled shells, but the West Indian worm shell is an exception. Its shell is thin, twisted, and tubelike. The first whorls curl regularly, but as the animal grows, the later whorls become progressively more uncoiled and distorted, so that no two specimens are identical. These marine snails are sequential ­hermaphrodites—they start their adult lives as free-living males, but later change sex and become sessile females, attaching themselves to various substrates such as sponges or other colonial animals.

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Angelwing Clam Many marine mollusks burrow into the sand or mud of the seabed to hide from predators. Others, like all members of this family of bivalves, the piddocks, are borers. They excavate permanent tunnels in mud, clay, limestone, wood, or even rock. They bore by a slow twisting movement of the valves, controlled by their muscular foot. The thin and usually elongate shell has a very rough surface on the front end that rasps into the substrate. Angelwing clams have strikingly beautifully white shells. They live in shallow, subtidal waters, boring in soft mud to depths of up to 1 meter. They are suspension feeders, feeding solely on plankton, and are usually found in scattered colonies of several dozen individuals.

Angelwing clam Cyrtopleura costata Distribution Massachusetts to Brazil Size 120 millimeters

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Pyramid clio Clio pyramidata Distribution Worldwide, open seas Size 10 millimeters

Pyramid Clio This small, fragile, and translucent shell belongs to a group of pelagic gastropods called pteropods. The world’s oceans are heavily populated with these small snails, which form part of the plankton. Pyramid clio provide a vital source of food for many small and large aquatic organisms. They are also named sea butterflies because the animal has two large, winglike extensions on its foot, which can be flapped like the wings of a butter­fly. Because their shells are exceptionally vulnerable to rising levels of carbon dioxide, these organisms have been proposed as bioindicators to monitor the effects of ocean acidification. Acidification occurs when oceanic waters absorb the atmospheric carbon dioxide released mainly from the burning of fossil fuels. At a certain threshold, the acidity dissolves the snails’ shells, and they, like many other mollusk species, cannot survive without their shell to protect them. 374

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Chambered Nautilus Nautiloids are the only group of living cephalopods with true external shells. The nautilus has a shell made up of chambers, which are connected by a tube called the siphuncle. The animal occupies only the last chamber of the shell, into which it can withdraw completely. As it grows, it creates a new larger chamber, using its 90 or so tentacles to move its body into the new space and sealing off the vacated one. Nautilus shells had been carved, etched, and engraved for many centuries. They rose to prominence in Europe during the 17th century when European craftsmanship reached new heights, particularly in the Netherlands. The carved shells were popular items in cabinets of curiosities and were among the most coveted natural history objects.

Chambered nautilus Nautilus pompilius Distribution Indo-Pacific Size 160 millimeters

Fly-specked moon snail Naticarius stercusmuscarum Distribution Mediterranean, Northwest Africa Size 30 millimeters

Fly-Specked Moon Snail Moon snails, or necklace shells, belong to a large family comprising several hundred species distributed throughout the world. They are an extremely diverse group that spans all marine habitats, from pole to pole, from the intertidal to the abyssal depths. These gastropods are active predators, feeding mostly on bivalves that live below the surface of the sand. After enveloping their prey with www.americanscientist.org

their disproportionately large foot, the snails drill a very neat circular hole through their victim’s shell in order to eat the animal inside. They use their radula to drill the hole and scrape away shell material, which is softened by a chemical secreted by an accessory organ. This method does not work every time, so the shells of prey species may be found with unsuccessful drill holes. 2023

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S c i e n t i s t s’

Nightstand

The Scientists’ Nightstand, American Scientist’s books section, offers reviews, review essays, brief excerpts, and more. For additional books coverage, please see our Science Culture ­blog channel online, which explores how science intersects with other areas of knowledge, entertainment, and society.

A Quantum History of SpaceTime

ALSO IN THIS ISSUE

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PERIPHERY: How Your Nervous System Predicts and Protects Against Disease. By Moses V. Chao. page 378

ONLINE On our Science Culture blog: www.americanscientist.org/blogs/ science-culture Trailblazing Women Botanists in the Grand Canyon Book review editor Jaime Herndon reviews Melissa L. Sevigny’s Brave the Wild River: The Untold Story of Two Women Who Mapped the Botany of the Grand Canyon.

From Brave the Wild River: The Untold Story of Two Women Who Mapped the Botany of the Grand Canyon.

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Chanda Prescod-Weinstein ON THE ORIGIN OF TIME: Stephen Hawking’s Final Theory. Thomas Hertog. 352 pp. Bantam, 2023. $28.99.

ast year, I had the opportunity to give a TED Talk on the main stage. A few days before the event, I had dinner with other people who would also be giving talks about science. As we settled in, a nuclear energy influencer (that’s a thing, I learned) asked me what I did. I explained that I’m a theoretical particle cosmologist, who mostly tries to understand what dark matter is. She looked at me with sincere confusion and asked, “How is that useful?” With On the Origin of Time: Stephen Hawking’s Final Theory, Belgian physicist Thomas Hertog offers a passionate rebuttal to those who think the only science that matters is that which has obvious and near-term material value. The answer to that influencer’s question? As Hertog writes, “Stephen’s final theory offers a powerful kernel of hope.” Braiding together the history of cosmology and the story of his working partnership with Hawking, Hertog contributes to the extensive literature for general audiences on the origins of the universe by offering, at heart, an homage to a beloved mentor. Hertog completed his doctoral work under the supervision of Hawking, which is explored in On the Origin of Time, and this led to an enduring research partnership that was still productive until nearly the end of Hawking’s life. The “final theory” mentioned in the book’s title addresses the ques-

tions that Hawking spent his entire career chasing: How did space-time begin, and what is a correct narrative of its evolution? Ultimately Hawking, in collaboration with Hertog and other scientists, came to the conclusion that in order to understand the past, we must begin with the present and understand that quantum mechanics means there is no such thing as a classical, linear past unfolding behind us. This top-down approach, as Hertog terms it, is antithetical to our typically taught and learned understanding about time. But for physicists, especially cosmologists, this perspective is nothing new. Our early training as relativists involves reconfiguring our conception of time as both relative and, under many circumstances of interest, mixing with space, to form space-time. Our training in quantum theory also teaches us that even the simplest physical systems do not necessarily have a deterministic evolution like the one that Newtonian physics promises us. In other words, we can calculate probabilities about the final state of a system, but we cannot guarantee it. What happens when you apply this idea to the whole universe at once? Hertog claims that, necessarily, one must land at a theory of quantum cosmology that he calls Hawking’s final theory. This means that we must let go of fixed notions of history where there is only one pathway to the past. In other words, we must shift away from deterministic notions of physical history. In trying to summarize the topdown model for this review, I faced a challenge that Hertog also had to confront head-on in his more than 300page text. A decent amount of background material is necessary in order to fully appreciate the ideas from which Hertog and Hawking drew to develop their no-boundary model of how the universe began. For exam-

ple, readers must understand that if we run our cosmological models—as described by Einstein’s gravitational equation—in reverse, we land at a mathematical singularity at time equal to zero. The jury is still out on whether this is a physical singularity—a phenomenon where space-time is no longer well-defined. At base, this is the problem that Hawking (who was also responsible for identifying it) spent the rest of his career investigating. We are not hopeless in this pursuit: The space-time singularities that arise in what we term classical cosmology potentially go away, or at least shift in nature, when we bring quantum mechanics into the picture. Hertog chooses to narrate these scientific questions largely through the frame of history, first by giving a chronological narrative of classical cosmology, then offering an introduction to how quantum gravity string theory provides fresh insights, before finally returning to the fundamental ways in which basic ideas and results from quantum mechanics encourage us to rethink absolutely everything. Before arriving at these historically infused (and almost exclusively menonly) introductions to the quantum and cosmological questions at hand, Hertog offers an extensive chapter on how Darwinian evolutionary theory reconfigured biology, providing insights from which Hertog and Hawking would later borrow. In my view, that promise is unfulfilled before the book is over, but it wasn’t overly bothersome to me. The question of how to interpret the history of our cosmos without the guarantee of determinism is a fundamentally profound question that will bother physicists in the best possible way, but will also be interesting and exciting to any curious person who has the right conditions to sit and wonder. Due to the way the book is set up and the order in which Hertog presents events and ideas, we don’t get to the cool ideas soon enough. The early excursion into evolution and biology could have been cut short, if not entirely. When I’ve asked colleagues about the ideas that Hertog advances at the very end of the book, some of them feel that the final theory is more vibes than substance, but I’m alright with that. I wish I had spent more of the book knowing what vibes we were going to land in, with a stronger sense of where www.americanscientist.org

Photo credit: Thomas Hertog and Jonathan Woods.

Thomas Hertog and Stephen Hawking worked together for nearly 20 years, exploring a new theory of physics and cosmology. After Hawking lost the ability to use his clicker, the two had a system of nonspeaking communication that included facial expressions.

Hertog was leading the reader. In addition, Hawking’s genius and reputation are so imposing on the text that Hertog himself disappears, to a certain extent. I find that unfortunate, because he is an accomplished scientist in his own right who has coauthored nearly 100 scientific papers—mostly with people who are not Stephen Hawking—on a range of topics that tackle major questions in theoretical cosmology. Overall the book is hagiographic in nature, but I struggle to impugn this. I also have scientific mentors, at least one of whom is mentioned in this book, about whom I would write only the most glowing words. While I could

have done without Hertog’s historical approach to narrating scientific ideas, On the Origin of Time works hard to capture some of the awe-inspiring spirit of Hawking’s A Brief History of Time, complete with extensive explanations and helpful figures. At the age of 10, I chose theoretical cosmology because I saw a documentary based on that bestseller; this book might do the same for someone else. Chanda Prescod-Weinstein is an associate professor of physics at University of New Hampshire and author of The Disordered Cosmos: A Journey into Dark Matter, Spacetime, and Dreams Deferred (Bold Type Books, 2021). 2023

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To Fix the Brain, Look to Other Nerves Sara Manning Peskin PERIPHERY: How Your Nervous System Predicts and Protects Against Disease. Moses V. Chao. 192 pp. Harvard University Press, 2023. $29.95.

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n 2015, thousands of researchers descended on a Chicago convention center for a gathering of the Society for Neuroscience. On the event’s second-to-last afternoon, Francis Collins, then-director of the National Institutes of Health, rose to the podium amid a standing-roomonly audience. The brochure promised a lecture about brain research.  By the time the talk ended, though, Collins was advocating for his listeners to explore something entirely different than what had been billed. The community of neuroscientists, he argued, should train its eye on the many neurons and networks that sit outside the brain and spinal cord. There, in the peripheral nervous system, lay some of the body’s most important, undiscovered clues to certain illnesses. Moses V. Chao, a professor at New York University and a former president of the Society for Neuroscience, was in the audience that day.  In his debut book, Periphery: How Your Nervous System Predicts and Protects against Disease, Chao heeds the call from the Chicago convention. His book

The peripheral nervous system relays messages between the brain and the spinal cord to the rest of the body. Because it doesn’t have the protections that the brain and spinal cord have, such as the skull or vertebral column and the blood-brain barrier, the potential for exposure to various toxins is increased.

misleading in its simplicity; in part because those nerves take on such varied assignments. They carry sensory information to the brain, convey

In the midst of peripheral nervous system dysfunction, we just might find a cure for diseases that, on the surface, appear to simply be problems of the brain. is a celebration of the peripheral nervous system, a 192-page biography of an underappreciated, overshadowed body part. The peripheral nervous system includes all nerves outside the brain and spinal cord. This definition is 378

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motor commands from the brain, and direct the automated functions of the heart, gut, and other organ systems.  In Periphery, Chao argues that these nerves are under-recognized sensors and controllers of human health and disease. To make his case,

he begins by explaining how the peripheral nervous system evolved long before the brain, in a tiny worm that roamed the deepest seas 600 million years ago. After touching on the gut-brain connection and the role of pain-sensing neurons, the bulk of Chao’s discussion focuses on the peripheral nervous system’s possible role in Parkinson’s disease and three other diseases. Although we think of Parkinson’s disease as being a problem in the brain—particularly in the deep cerebral regions that modulate ­m ovement—Chao writes convincingly that the condition may actually begin in the nerves of the gut. One of the earliest symptoms of Parkinson’s disease is constipation, which often starts years before the stereotypical trembling and stiffness. Lewy bodies, the microscopic hallmark of

Parkinson’s disease in the brain, can also be found dotting the nerves that run along the gastrointestinal tract. Patients who have undergone an appendectomy are less likely to develop Parkinson’s disease, suggesting that the vestigial appendage may be an early pathologic hideout. The vagus nerve even serves as a likely suspect when it comes to explaining how a brain disease could start outside the head. This beefy structure, which runs from the abdomen into the skull, may serve as an anatomical highway for pathologic proteins to make their way from gut to brain. Chao eventually asserts that the peripheral nervous system has been taken for granted because its work is done subconsciously.  When we pet a dog, we don’t have to tell the cells in our fingertips to communicate the feeling of fluffiness to our brain. But when these processes go awry, producing chronic pain or opening the gates for neurodegeneration, we should pay attention. Chao claims that, in the midst of peripheral nervous system dysfunction, we just might find a cure for diseases that, on the surface, appear to simply be problems of the brain.  Periphery moves at a rapid clip, touching on many topics, perhaps at the expense of extended discussion, but it still stops along the way for brief portraits of some of the greatest researchers in the history of neuroscience. Jean-Martin Charcot coined names for at least 12 neurologic disorders, including multiple sclerosis, Tourette syndrome, and amyotrophic lateral sclerosis (ALS). A talented sketch artist, Charcot discerned disease patterns by seeing commonalities in his patients’ postures and expressions. Rita Levi-Montalcini, another scientist portrayed in the book, conducted research in a bare-bones laboratory in her bedroom during World War II, when she was prohibited from working in Italian universities because she was Jewish. She went on to win a Nobel Prize for discovering a protein that helps nerves grow. Although the subtitle of Periphery makes clear that science is the main focus, rather than the scientists, the recurring cast of characters enriches the text and conveys how interconnected the world of neuro­science really is. Chao’s book is a sweeping tour that caters primarily to those with a

The Power of Data Literacy Back-to-school season is well underway, and with the recent focus on increasing students’ ability to utilize evidence-based decision-making, one core curriculum standard that is emphasized by high school teachers is data literacy. That’s a key theme in the graphic novel Power On! written by Jean J. Ryoo and Jane Margolis and illustrated by Charis JB. What happens when a supposedly objective AI system is actually racially biased, and causes real harm

in the community? Can an algorithm be racist? That’s what a diverse group of friends decides to find out in this timely story. Growing up around tech, they’ve always felt pretty tech-savvy—but after the AI incident, suddenly they’re not so sure. The friends decide they want to learn more about computers by taking some computer science classes at their various high schools, but with mixed results. Although some of the friends have teachers who

Reprinted with permission from The MIT Press. Copyright 2023

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Excerpted from Power On! By Jean J. Ryoo and Jane Margolis. Reprinted with permission from The MIT Press. Copyright 2023.

background in neuroscience. The text moves quickly from one topic to the next, often delving into arcane medical details, so lay readers may find themselves adrift amid the terminology and the nonlinear narrative. Nevertheless, Chao proves to be a capable guide, and at many points it feels as if he is a personal mentor sitting at the front of a small classroom, expounding on his years of experience.  380

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The final note in Periphery feels almost futuristic.  Efforts to induce neurons in the brain to regenerate have proven slow-moving despite significant funding, in part because these nerves produce proteins that impede regrowth.  For the solution, Chao proposes we look to the peripheral nervous system, where damaged neurons regrow successfully all the time. “The periphery holds the

discuss issues of equity in technology and take them on field trips to local companies, others have instructors who only teach typing and basic website setup. Some of the kids are even shut out of classes entirely and told they’d be “better off” learning other subjects. After-school computing clubs fill in some of those gaps, teaching the students about programming wearable tech. In the excerpt shown here, the friends have determined they need to take a more active role in accessing computer science education. They have taken a teacher’s suggestion to present at their local school board meeting, and in order to prepare, they have decided to call all the schools in their district to see which even offer computer science. The students need to effectively present their data, as well as support their point with statistics about the demographics of students who enroll in these classes. Ryoo and Margolis hope that this story will inspire students to investigate their own districts’ offerings, and encourage them to take an active role in increasing access to classes. Teachers could take this story and create a project in which students decide on a local problem about which they have to gather, analyze, and ­present data. Ryoo and Margolis have created a fun and engaging story that explores the importance of computing and data education, biases in education, issues in equity and ethics in tech, and much more. Braiding together the stories of these friends with explainers on computer science and profiles of people of color and women in tech, this book is highly informative for young people wanting an accessible intro to computer science and tech. —Fenella Saunders

answers for regeneration,” he states passionately, adding later that he sees the peripheral nervous system as the key to extending lifespan. Let’s hope he’s right. Sara Manning Peskin is an assistant professor of clinical neurology at the University of Pennsylvania. She is the author of A Molecule Away From Madness: Tales of the Hijacked Brain (W.W. Norton & Co, 2022), a New York Times Editors’ Choice.

November–December 2023

Volume 32 Number 06

Sigma Xi Today A NEWSLETTER OF SIGMA XI, THE SCIENTIFIC RESEARCH HONOR SOCIETY

Sigma Xi Elections Begin November 13 Active Sigma Xi members will receive a ballot from [email protected] to begin voting in the 2023 Sigma Xi elections. All members who receive a ballot can vote for the president-elect, as well as for other open positions in their chapter’s region and constituency. Members who aren’t affiliated with a chapter can vote for candidates in the Membership-at-Large Constituency Group. Ballots will be personalized with the candidates who pertain to each member. President-Elect — Three-year term beginning July 1, 2024: the first year as president-elect, the second year as president, and the third year as immediate past president. Directors — Three-year term beginning July 1, 2024. Director positions up for election serve the Baccalaureate Colleges Constituency Group, Canadian/International Constituency Group, Northwest Region, and Southeast Region. Associate Directors — Three-year term beginning July 1, 2024. Associate director positions up for election serve the Membership-at-Large Constituency Group, Research & Doctoral Universities Constituency Group, North Central Region, and Southwest Region. Representatives on the Committee on Nominations — Three-year term beginning immediately after the election. Representative positions up for election serve the Comprehensive Colleges & Universities Constituency Group; Mid-Atlantic Region; Northeast Region; and Area Groups, Industries, State & Federal Labs. Visit sigmaxi.org to learn more about the 2023 election candidates and position responsibilities. Sigma Xi Today is managed by Jason Papagan and designed by Chao Hui Tu. www.americanscientist.org

From the President Of Mice and Mental Health In the world of mice, with whom humans share a common ancestor according to one theory of evolution, an interesting experiment was performed more than 15 years ago. In the experiment, a mouse is confronted with two paths: one leading directly to chocolate, the other leading to a second mouse whose access to the chocolate can only be facilitated by the first mouse. After some hesitation (that we still refuse to call moral thinking), the first mouse invariably chooses the second door to help the fellow mouse, and they go to eat the chocolate together. The liberator mouse displays empathy. It also shares its own assured food supply. Subsequently, the mouse acquires an ally, so this decision is also profitable. I also recall the story of John Jay O’Connor, late husband of Sandra Day O’Connor, the first female associate justice of the U.S. Supreme Court. While living in a care facility due to his progressing Alzheimer’s disease, he developed a relationship with another woman at the facility. Surprisingly, it was reported that his wife was happy with the comfort he had found, an empathetic acknowledgment that patients with Alzheimer’s disease sometimes develop new romantic relationships as their old ones fade from memory. It warms my heart that this couple enjoyed mutual emotional support, alongside a rare level of compassion and understanding from the former justice. I reference these stories to reflect on some of our current moral compasses: humanity, empathy, and support of mental health. This fall, the campus of the University of North Carolina at Chapel Hill experienced multiple traumatic events, including the fatal shooting of a faculty advisor in the department of applied physical sciences. With Sigma Xi’s headquarters right down the road in Research Triangle Park, the safety and well-being of our local members became one of our top concerns. That month, Sigma Xi scheduled a special emotional health workshop with our wellness partner, Happy. These recurring support sessions have been offered as a benefit to all members since 2021, when stress and loneliness were skyrocketing for many during the COVID-19 pandemic. We continue our dedication to supporting our members across the country— not just through grants, awards, and career development, but also through investing in their emotional well-being. As scientists, we know we can learn a great deal from lab mice. However, all too often we only look at scientific data and experimental results. But if we look a little closer, a seemingly empathetic mouse may have something more to teach us (or remind us) about companionship and humanity.

Marija Strojnik

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MEMBERS AND CHAPTERS

Shirley M. Tilghman Receives 2023 Sigma Xi Gold Key Award

Sigma Xi, The Scientific Research Honor Society is honored to announce that Shirley M. Tilghman, PhD, is the 2023 recipient of the Gold Key Award. As the Society’s highest and most prestigious honor, the Gold Key Award is presented to a member who has made extraordinary contributions to their profession and has fostered critical innovations to enhance the health of the research enterprise, to cultivate integrity in research, or to promote the public understanding of science for the purpose of improving the human condition. Dr. Tilghman will be recognized on November 11, 2023, in Long Beach, California, during the awards banquet at Sigma Xi’s annual conference, the International Forum on Research Excellence (IFoRE). “In addition to being a generational molecular biologist, Shirley Tilghman has forged one of the most respected careers in higher education,” said Marija Strojnik, president of Sigma Xi. “Her

accomplishments as an institutional leader, paired with her commitment to advancing STEM education and early career science, make her an exceptional recipient of Sigma Xi’s highest honor.” A prominent molecular biologist, innovator, and educational leader, Dr. Tilghman is president emerita and professor of molecular biology and public affairs at Princeton University. A pioneer in research on genetics and genomics, Tilghman was a leading adviser to the National Institutes of Health (NIH) for the Human Genome Project. In addition to serving as Princeton’s president from 2001 to 2013, she was named to Harvard University’s principal fiduciary governing board, the Harvard Corporation, in 2015, where she still serves today. A native of Toronto, Dr. Tilghman received her bachelor of science degree from Queen’s University in Kingston, Ontario, in 1968. After two years of secondary school teaching in Sierra Leone, she earned her PhD in biochemistry from Temple University in Philadelphia. She did postdoctoral work at the NIH and contributed to many scientific breakthroughs as an independent investigator at the Institute for Cancer Research in Philadelphia. In 1986, she began her career at Princeton as the Howard A. Prior Professor of the Life Sciences. Over the next 15 years, she held many additional council and leadership positions at Princeton before being named pres-

ident in 2001. Tilghman’s exceptional contributions to science have earned her many awards, including the 2002 L’Oréal-UNESCO for Women in Science Award, the 2003 Lifetime Achievement Award from the Society for Developmental Biology, and the 2007 Genetics Society of America Medal. In addition to her reputation as a distinguished scientist and researcher, Tilghman has been a nationally recognized leader and advocate throughout her career on behalf of women and young scientists. She has chaired organizations and authored recent publications focused on educational reform, the importance of diversity, equity, and inclusion in science, and promoting efforts to make the early careers of young scientists as meaningful and productive as possible. The symbolism of the Gold Key Award pays homage to the early days of Sigma Xi (late 1800s to early 1900s), when induction into the Society was often accompanied by the presentation of a small gold key. The key was routinely attached as a charm to a bracelet or chain that held a pocket watch, which was the style of the day, and represented pride in the science or engineering accomplishments of the holder. Previous recipients of the award include Bruce Alberts, Shirley M. Malcom, Walter E. Massey, Gordon E. Moore, and Norman R. Augustine.

Session Spotlights: IFoRE ‘23 IFoRE ’23 will include a packed agenda with scientific thought leaders, award winners, and compelling session themes including research ethics, science policy, climate change, artificial intelligence, nanotechnology, genome editing, science communication, grant writing for students, and more! Visit experienceIFoRE.org/agenda to view the full conference agenda.

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Florida’s Ecological Crises and How They May Inform Our Future James Sullivan Florida Atlantic University

Teaching Ethics in AI: A Practical Workshop for Educators Richard Whittington Tuskegee University

Our Future in Science: A STEM Education Model from Young People at the Intersection of Science and Social Justice Jylana Sheats Aspen Institute

Shifting Demographics in STEM Fields Through Community College Research Programs Jackie Swanik Wake Technical Community College

Sigma Xi Today

PROGRAMS

of GIAR: Abhinav Sur Grant: $1,000 in Spring 2018 Education level at time of the grant: PhD student Project Description: The main goal of my project was to understand the potential genetic regulatory modules and differentiation trajectories underlying the diversification of cell types during embryogenesis in the annelid Capitella teleta. For that purpose, I captured single cells from Capitella larval stages and sequenced them to generate a single cell atlas of all genes expressed per cell in the whole larval body plan at two developmental stages. Our whole-organism scRNA-seq analysis generated comprehensive insights into metazoan cell-type evolution and tissue-specific genome-wide regulatory networks. This was one of the first attempts using such a systems-biology approach to answer developmental biology questions in the light of evolution. The Sigma Xi grant was highly instrumental in enabling me to perform such high-throughput experiments, which are generally quite expensive. I used the grant money to perform the actual microfluidic capture of single cells and to sequence the single-cell transcriptomes. How did the grant process or the project itself influence you as a scientist/researcher? The grant process and this project in particular greatly enhanced my motivation to become a scientist. For a long time, I’d had ambitions of using single-cell omics to answer evolutionary developmental biology questions; however, I was discouraged by the lack of funding and facilities at my university. The Sigma Xi grant was a huge push for me to accumulate funding from various sources to make this project possible. Where are you now? Right now, I am a postdoctoral research scholar at the National Institutes of Health, where I am using single-cell omics approaches to uncover cell-fate specification and to differentiate on during zebrafish development.

Congratulations to Sigma Xi’s 2023 Award Winners Sigma Xi, The Scientific Research Honor Society is proud to announce its 2023 Award Winners. Presented annually by the Society’s Prizes and Awards program, the awards recognize exemplary achievement in science and engineering. Recipients are presented with the awards at the International Forum on Research Excellence (IFoRE), where most will be plenary speakers. This year’s conference will be held November 10–12, 2023, in Long Beach, California. More information on each recipient can be found at experienceIFoRE.org/award-winners.

John P. McGovern Science and Society Award

Young Investigator Award

Ken Miller, PhD Brown University

Maryam Naghibolhosseini, PhD Michigan State University

William Procter Prize for Scientific Achievement

Walston Chubb Award for Innovation

Evan Ferguson Award for Service to the Society

John A. Rogers, PhD Northwestern University

Xin Zhang, PhD Boston University

Malgosia Wilk, PhD University of Texas at Arlington

www.americanscientist.org

2023 November–December 383

EVENTS

Announcing the 2023 Cohort of Sigma Xi Fellows Sigma Xi is proud to announce the 2023 cohort of Sigma Xi Fellows. They will be recognized during the second annual International Forum on Research Excellence (IFoRE) taking place November 10–12, 2023, in Long Beach, California. The Fellow of Sigma Xi distinction is awarded on a competitive basis to members who have been recognized by their peers. Fellows must be an active (dues-paying) full member for the past 10 years continuously, or a life member, with distinguished service to Sigma Xi and outstanding contributions to the scientific enterprise. Learn more about the 2023 Fellows and how to nominate members for future cohorts by visiting sigmaxi.org/fellows.

Diane Birt Iowa State University

Digvir Jayas University of Manitoba

Robert Horton University of California, Berkeley

Liovando Marciano da Costa Membership-atLarge

Frank Abrams North Carolina State University

Shekhar Bhansali Florida International University

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Sigma Xi Today

Charles Rice Kansas State University

Gary Shueng Han Chan Hong Kong University of Science and Technology

Norman Augustine Princeton University

Kimberly Carlson University of Nebraska at Kearney

Philip Wyatt University of California, Santa Barbara

David Flannigan University of Minnesota

David Allison Indiana University

Jonathan Clark Weber State University

Robert Youker Western Carolina University

Akhlesh Lakhtakia Pennsylvania State University

Stan White Orange County, California

Michael Madden University of North Carolina at Chapel Hill

Call for Nominations 2024

William Procter Prize Sigma Xi’s highest honor is awarded to a scientist who has made an outstanding contribution to scientific research and has demonstrated the ability to communicate this research to scientists in other disciplines.

John P. McGovern Science and Society Award The McGovern award recognizes a scientist or an engineer who has made an outstanding contribution to science and society.

SIGMA XI PRIZES & AWARDS Deadline for nominations is January 31

Do you know a scientist or engineer who should be recognized for their commitment to scientific research excellence? Sigma Xi invites nominations for the following awards that recognize achievements in science or engineering research and communication. Nomination guidelines and eligibility can be found at sigmaxi.org/awards. Submissions should be sent by email to [email protected].

Walston Chubb Innovation Award The Walston Chubb Award honors and promotes creativity in science and engineering.

Young Investigator Award Honors outstanding early career researchers across life, physical, and social sciences. Nominees must be within ten years of their highest earned degree at the time of nomination.

Submitataion! Nomin [email protected] sigmaxi.org/awards

Xin Zhang

Walston Chubb Innovation Award, 2023

Maryam Naghibolhosseini Young Investigator Award, 2023

John A. Rogers

William Procter Prize, 2023

Kenneth R. Miller

John P. McGovern Science and Society Award, 2023